API stands for "application programming interface". It refers to the definitions and protocols that allow one application to communicate with another. In Urbit, some notable APIs are the tasks and gifts of vanes (kernel modules) and things like pokes for Gall agents.
Further reading
- The Arvo reference docs: These technical developer docs include API documentation for Arvo's vanes.
- App School: This is a guide to writing Gall agents, and goes over the APIs of Gall agents in detail.