The simplest way to think about it
An API is a menu. The kitchen decides what can be ordered, describes each dish, and states what arrives. You cannot order something that is not on the menu, and you cannot walk into the kitchen.
That restriction is the point. The API is how a system offers capability without giving away control of its database.
What does REST mean?
REST is the most common style for web APIs. It maps operations onto addresses and verbs: GET to read, POST to create, PATCH to update, DELETE to remove. A request to read a customer looks like a URL plus a credential; the response comes back as structured data, usually JSON.
What business owners should actually ask
- Does the API cover the data I need, or only part of it?
- Can it write, or only read?
- Are there rate limits that would break a bulk import?
- How is access authenticated and revoked?
- Is there a webhook for events, or must we poll for changes?