API
Application Programming Interface
In short
An API is a fixed, agreed way for two programs to talk to each other, so they can fetch and send data without a person in between.
Think of an API as the hatch at a café. You do not walk into the kitchen. You order at the hatch, from a menu, and get back what you asked for. When your website takes card payments, shows a map or adds a new customer to another system, it nearly always happens through an API.
When it becomes your concern
As soon as you have two systems that ought to talk to each other. A contact form that puts the enquiry straight into your CRM system, or an online store that updates the stock in your accounts. Without an API, you are the one copying between two windows. With an API, the job can be done by an integration.
An API is also a question of who is in charge. The supplier can change it, charge for it or shut it down. And a system without an API is a dead end the day you want to connect something to it.
Check this before you buy your next system
If you are choosing a new booking, accounting or customer system, search for its name plus "API" or "integrations". If you find a public documentation page, other systems can be connected later. If you find nothing, ask the supplier directly before you sign.
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