flowchart TB cust(["Customer"]) agent(["Support Agent"]) sys["Order Management<br/>the system being described"] pay["Payment Gateway<br/>external SaaS"] erp["ERP<br/>existing on-premises"] mail["Email Provider<br/>external SaaS"] crm["CRM<br/>external SaaS"] cust -->|"places and tracks orders"| sys agent -->|"amends and refunds orders"| sys sys -->|"authorises and captures"| pay sys -->|"posts financial documents"| erp sys -->|"sends confirmations"| mail sys -->|"reads account and entitlement"| crm
System Context Diagram
The single box of your system surrounded by the people and external systems it talks to, and nothing about how it is built inside.