Short answer
An API (application programming interface) is the way programs talk to each other. It is like a "door" into a system through which another program can securely request or send data — for example, an online store sends an order to accounting, or a website gets an exchange rate. Without an API, data between programs has to be copied by hand.
A simple example
Imagine a restaurant. You (the program) don’t walk into the kitchen (the other system) — you order from the waiter (the API). The waiter knows what can be ordered, passes the order to the kitchen and brings back the result. The API defines which “dishes” can be ordered and in what form.
Where businesses use APIs
- The online store passes orders to the warehouse and accounting.
- The website takes payments through a payment provider’s API.
- The CRM checks company details in a register.
- An AI agent accesses your systems through their APIs.
Why an API matters when choosing software
If a program has a good API, it can be connected to other systems and automated. If there’s no API, the data stays “locked in”, and all that’s left is export and import or fragile workarounds such as RPA.
The most common kind of API is a REST API. Access is usually protected with an API key.