An API is a set of specific doors, and each door has one job. In a REST API, an endpoint usually looks like a URL path: one for customers, one for invoices, one for a specific invoice by ID. The HTTP method is the verb you say at that address: read, create, update, or delete. A webhook‘s receiving URL is an endpoint too, one that waits for another system to send it information.
Imagine a service desk with different windows. One handles new applications, one handles payments, one handles address changes, one handles cancellations. The building is the whole operation. Each window is one endpoint, and you have to walk up to the right one with the right form.
Why you care
If someone says “we need to call the API,” the next question is “which endpoint?” An agent pulling invoices, creating a deal in a CRM, or posting to Slack is calling endpoints under the hood, and the wrong window, or the wrong shape of information, gets rejected. “Connect these tools” always means a set of specific windows the software has to use correctly, one request at a time.