Difference between an endpoint and a port in SQL Server
I like to think of it as the endpoint being the "SQL Server side" part of what a client connects to. There are endpoints for TCP (probably the one you refer to), Named Pipes and Shared Memory. Those are the regular endpoints that a client application connects to. You can, for instance, set privileges on an endpoint, allowing login A to connect to TCP and B connect to Shared Memory (not that I've ever had the need for this). The endpoint is implemented by a DLL (I usually refer to all this as "NetLib", and for TCP and Named Pipes exposed through a port.

Then there are endpoints for mirroring and the old SOAP web-methods as well.