Endpoints
A simple mental model to understand 'Endpoints' in LLM Stack is to think of them as our age old REST APIs. The only difference is that, these endpoints are powered by AI and instead of writing a business logic for each API, you can simply instruct the model to do a specific task on the input data and it will do it for you.
Now, any REST API has a defined output format, similarly, each endpoint in LLM Stack has a defined output format and can be designed by the user itself.
Tl;dr: Endpoints are simple REST APIs which are one-shot or few-shot LLM calls to do a specific task on the input data and return consistent required output format.