Platform API
The programmatic contract through which teams consume platform capabilities, and the thing that must stay stable while everything behind it changes.
Whether the interface is a YAML manifest, a CLI, a REST endpoint or a set of custom resources, it is an API, and it should be designed with the same seriousness as an external one — because the cost of breaking it is paid by every team in the organisation simultaneously.
Designing it well means the same disciplines: explicit versioning, additive change by default, deprecation with notice, and a contract that describes intent rather than implementation. That last point is what preserves the platform's freedom to change: a manifest saying a service needs a relational database with a given size and availability class lets the platform migrate engines, regions or providers underneath; one that names the specific managed product and its parameters has published the implementation as the contract and can never move.
The corollary is that a platform's most valuable asset is its interface stability, and its most common self-inflicted wound is leaking implementation detail into the interface early, when the first consumer needed one specific thing and it was quicker to expose it directly.