Terminology

454 terms, tools, patterns and metrics an architect is expected to use precisely. Each one gets a short explanation of what it is, and — where it matters — what it is commonly confused with. Search filters as you type; the column headers sort.

All areas454 Architecture Fundamentals16 Distributed Systems73 Data Architecture71 Cloud Architecture55 Networking13 API & Integration Architecture17 Reliability & Resilience16 Observability14 Performance & Capacity Engineering13 Security Architecture50 Cost Architecture & FinOps12 Business Architecture9 Architecture Communication8 Enterprise Architecture8 Legacy Modernization11 AI-Era Architecture15 Software Architecture & Engineering19 Architecture Patterns15 Architecture Decision-Making11 The Architect's Meta-Skills8

Kind Any concept166 practice107 pattern93 case-study26 tool26 protocol22 metric14

454 terms shown.

Term	Kind	Topic	What it is
Data Retention Policy	practice	Data Architecture	A defined rule for how long each class of data is kept, where, and what happens at the end of it.
Data-Flow Diagram DFD	practice	Architecture Communication	A diagram of how data moves between processes, stores and external entities, with trust boundaries drawn on it.
Database Index	concept	Data Architecture	A secondary structure that lets the engine find rows without scanning, trading write cost and storage for read speed.
Database per Service	pattern	Polyglot Persistence	Each service owning its own datastore, with no other service reading or writing it directly.
Dead Letter Queue DLQ	pattern	API & Integration	A separate queue that receives messages which could not be processed after a set number of attempts, so they neither block the consumer nor disappear.
Deadline Exceeded	concept	Timeouts & Deadlines	The error returned when a request's overall budget expires — semantically distinct from a per-hop timeout, and a signal that must not be retried blindly.
Decision-Making Under Uncertainty	practice	Meta-Skills	Choosing well when the information is incomplete — by bounding the downside and buying information, rather than by waiting for certainty.
Delivery vs Maintainability Short-term Delivery vs Long-term Maintainability, Speed vs Quality	concept	Architecture Decision-Making	Choosing where to take deliberate shortcuts, based on which kinds of debt are cheap to repay and which compound.
Denormalisation	practice	Data Architecture	Deliberately duplicating data across records to make reads cheap, accepting the write-time cost of keeping copies in step.
Disaster Recovery DR	practice	Reliability & Resilience	The plan and capability for restoring service after an event that takes out a whole site, region or system.
Discord's Message Store Migrations	case-study	Data Architecture	Discord moved from MongoDB to Cassandra to ScyllaDB as message volume grew from millions to trillions, each time for a specific and different reason.
Distributed Tracing	tool	Observability	Following one logical request across every service it touches by propagating a shared trace identifier and recording timed spans.
DNS Domain Name System	protocol	Networking	The distributed directory that resolves names to addresses, and a surprisingly load-bearing part of most architectures.
Document Store	tool	NoSQL Stores	A store that keeps semi-structured documents — typically JSON — retrievable by key and queryable by their contents.
Domain-Driven Design DDD	practice	Software Architecture	Modelling software around the business domain, with boundaries drawn where the language of the business changes.
DORA Metrics Four Key Metrics	metric	Software Architecture	Four measures of software delivery performance — deployment frequency, lead time for change, change failure rate, and time to restore service.
Dropbox's Move Off S3 Magic Pocket	case-study	Cost & FinOps	Dropbox moved the majority of its file storage off Amazon S3 onto custom infrastructure, reporting savings that its S-1 filing put at roughly $75 million over two years.
Dual Write	pattern	Data Migration Strategies	Writing the same change to both the old and new stores during a migration, and the reconciliation that makes it trustworthy.
Durability vs Availability	concept	Cloud Storage	Two different storage guarantees — whether data survives, and whether it can be reached right now — routinely conflated because both are quoted in nines.
Dwell Time Mean Time to Detect	metric	Security Incident Response	The period between an attacker gaining access and being detected — the metric that determines how much damage an intrusion can do.
Dynamic Secrets	pattern	Secrets Management	Credentials generated on demand for a specific consumer with a short lease, rather than stored, shared and rotated periodically.
eBay's Architectural Generations	case-study	Legacy Modernization	eBay rewrote its core platform several times across its first decade, each time because the previous generation had hit a limit that could not be tuned away.
Edge Function	concept	Edge Computing	Code executed at a CDN point of presence close to the user, in a constrained, fast-starting runtime, typically to modify or route a request before it reaches an origin.
Egress Cost Data Transfer Out	concept	Cost & FinOps	The charge for moving data out of a cloud provider or across its zones and regions — usually the least-anticipated line on a cloud bill.
Egress Filtering	practice	Network Security	Restricting which destinations a workload may connect to outbound — the control that limits data exfiltration and SSRF impact, and the one most often omitted.
Egress Path Analysis	practice	Network & Egress Costs	Tracing where data physically moves in an architecture, because transfer charges follow paths that appear nowhere on the diagram.
Embedding	concept	AI-Era Architecture	A dense numeric vector representing a piece of content, positioned so that semantically similar content sits nearby.
Encapsulation	concept	Architecture Fundamentals	Keeping a component's state private, so it can only be changed through operations that maintain its invariants.
Encryption at Rest and in Transit	practice	Security Architecture	Protecting stored data from disclosure if the medium is obtained, and network data from disclosure if the path is observed — two different controls against two different threats.
Enterprise Integration Patterns EIP	practice	API & Integration	A catalogue of named, composable messaging patterns — router, translator, aggregator, splitter, filter, dead letter channel — that gives integration work a shared vocabulary.
Envelope Encryption	pattern	Encryption	Encrypting data with a locally-generated data key, then encrypting that key with a master key held in a key management service, and storing the wrapped key alongside the ciphertext.
Error Budget	metric	Reliability & Resilience	The amount of unreliability an SLO permits, treated as a resource that feature velocity spends.
Error Budget Policy	practice	Error Budgets	The written agreement about what happens when the error budget is exhausted, which is what turns an SLO from a number into a control.
ETL vs ELT	concept	Data Architecture	Whether data is transformed before loading into the target or after it, which decides where the compute happens and how much raw history you keep.
Etsy's Continuous Deployment	case-study	Software Architecture	Etsy moved from infrequent, risky releases to dozens of deploys a day, demonstrating that deployment frequency and stability improve together rather than trading off.
Event Sourcing	pattern	Data Architecture	Storing the full sequence of state-changing events as the system of record, and deriving current state by replaying them.
Event Store	tool	Event Sourcing	An append-only store of domain events organised into per-entity streams, serving as the system of record rather than as a log beside it.
Event Stream	tool	Distributed Systems	An append-only, retained log of events that many independent consumers read at their own position, and can re-read.
Event Upcasting	pattern	Event Sourcing	Transforming an old event's stored form into the current shape as it is read, so historical events remain replayable after the schema changes.
Event-Driven Architecture EDA	pattern	Architecture Patterns	A style in which components communicate by emitting and reacting to facts about what happened, rather than by calling each other.
Event-Driven Integration	pattern	API & Integration	Systems integrating by publishing and consuming events rather than by calling each other's APIs.
Eventual Consistency	concept	Distributed Systems	A guarantee that replicas will converge to the same value if updates stop, with no bound on how long reads may be stale.
Evolutionary Architecture	practice	Architecture Fundamentals	Designing for guided, incremental change rather than trying to get the structure right once, up front.
Exponential Backoff	pattern	Distributed Systems	Increasing the wait between retries geometrically, with random jitter, so that failures do not synchronise into a stampede.
Fail-Fast vs Fail-Safe	concept	Failure Modes	Whether a component should stop immediately on detecting a problem, or continue in a degraded but safe mode — a choice that depends entirely on which outcome is worse.
Failback	practice	Disaster Recovery	Returning to the primary region after a failover, including reconciling the data written while it was unavailable — the half of DR that is usually unplanned.
Failure Thinking	practice	Meta-Skills	Making "what happens when this fails?" a standing question applied to every component and every dependency in a design.
Failure Threshold	concept	Circuit Breakers	The condition that trips a circuit breaker — best expressed as a failure rate over a rolling window with a minimum request volume, not as a consecutive-failure count.
Fallback Strategy	pattern	Circuit Breakers	What a caller does instead when a circuit breaker is open — the part of the pattern that determines whether failing fast helps anyone.
Fan-Out	concept	Distributed Systems	One incoming request causing many outgoing ones, which multiplies both load and tail latency.
Fault Tolerance	concept	Distributed Systems	Continuing to operate correctly despite the failure of some components, by design rather than by luck.
Feature Flag Feature Toggle	pattern	Software Architecture	A runtime switch that decouples deploying code from releasing behaviour, so unfinished or risky work can ship dark.
Feature Parity Trap	concept	Rebuild vs Re-architect	The expectation that a replacement system must match every behaviour of the old one before it can be adopted, which is what makes rewrites never finish.
Fencing Token	pattern	Leader Election	A monotonically increasing number issued with leadership or a lock, checked by the resource, so writes from a deposed holder are rejected.
Field-Level Encryption Application-Level Encryption	pattern	Encryption	Encrypting specific sensitive fields in the application before they reach the datastore, so the store never holds plaintext.
Figma's Postgres Sharding	case-study	Data Architecture	Figma delayed sharding for years using replicas and vertical partitioning, then sharded Postgres horizontally without downtime using logical shards and a proxy layer.
FinOps	practice	Cost & FinOps	The practice of giving engineering teams visibility into and accountability for the cost of what they build and run.
First-Principles Reasoning	practice	Meta-Skills	Reducing a problem to the physical, mathematical or economic facts it rests on, then reasoning up, rather than reasoning from analogy or convention.
Fitness Function	practice	Architecture Fundamentals	An automated check that an architectural characteristic still holds, run continuously rather than reviewed occasionally.
Foreign Key Constraint	concept	Relational Modelling	A database-enforced rule that a referencing value must exist in the referenced table — referential integrity that no application bug can violate.