In layman’s terms, it is a language used among various applications. For example, you can add your Twitter handle on the sidebar of your WordPress blog without any coding and it is just because WordPress uses the Twitter API that lets you do it. The APIs have been in use by developers, programmers, and their clients for a few decades now and are set to stay.
https://www.getastra.com/blog/knowledge-base/api-security-testing/
