In detail
An API (Application Programming Interface) is a set of rules that lets one piece of software request data or actions from another. A mobile app talking to a server, a website pulling stock from a warehouse system, and a payment gateway confirming a transaction all rely on APIs.
Most modern business software is built as a set of APIs with different front ends on top, which is why integration work is a large part of custom development.
How this relates to our work
API comes up most often in our custom solutions work. Business automation, internal systems and integrations for processes that off-the-shelf software does not fit.