API stands for “Application Programming Interface.” It’s a set of rules that software programs use to talk to each other. When you visit a website, your web browser talks to the website’s server using the API.

Your web browser also uses the API to talk to your computer’s operating system. For example, when you click on a link, your web browser asks your operating system to open the link.

API signatures are used to identify different software programs. Each program has its own unique signature that identifies it. This is how your computer knows which program to use when you open a file or visit a website.