API stands for Application Programming Interface. This is a general term for programming techniques that are available for software developers when they integrate with a particular service or application. These techniques vary on the software type and may include web API, remote API, SDKs, libraries, frameworks, and much more.
In the payments industry, APIs are usually provided by any party participating in the money flow (e.g. payment gateways, processors, service providers) to facilitate the money transferring process. Adyen uses the most reliable and secure API, allowing its merchants to integrate with Adyen services using Client-Side Encryption, Hosted Payment Pages, and other modern techniques.