openapi-glossary
OpenAPI Glossary
To avoid confusion in the creation of educational material, tooling, and other content, having a shared vocabulary is important. A lot of people in the OpenAPI community call a lot of things a lot of different things, so let's take a swing at unification here.
API
The general definition "Application Program Interface" can mean a lot of things, with different types of interface. OpenAPI is specifically talking about HTTP-based APIs, which in general is anything REST, RESTish, and many generic types of RPC.
API-First
When APIs first started getting popular, a lot of companies started flopping them out as a marketing ploy. These APIs were generally not particularly useful, rarely performant, and frustrating to work with.
"API First" is a concept that teams should build the APIs first, and make them something they would want to work with, therefore solving useability issues, performance issues, etc. and supposedly creating a better experience for their customers.
API Description
Aliases include: "API Definition" or "API Contract".