An API is a series of conventions or routines used to access software functions. Most major search products have an API program.

An interface that can be used by third-party program developers to add member-specific data to applications. When companies open their platforms to third-party developers, they can host APIs in the same way that companies such as Facebook and MySpace do. The applications created using APIs are also called widgets, and can be installed by users so they can use them on their social network profiles.