An endpoint, as I imagine they may be using it
in this course, is simply a route defined by your
rails application. In terms of an API (which can
mean many things and is worth further research on
your part), hitting that endpoint will serve up a
resource from your application, or perform some
form of action. An example may explain this
Say we have an application that handles users
and we want our API to expose the users resource.
If we follow RESTful convention for our API we
will expose seven distinct 'endpoints' linked to
seven distinct 'actions' (index, show, create,
update, destroy, new, edit) surrounding users.
When building our API, we would make is so
anyone who visits "www.myapp.com/users" via a get
request is returned some data representation of
all users in our application. "/users" is the
endpoint. Likewise performing a post action to
"/users" with valid data is how we create new
users. "/users" is still the endpoint but under
different context. If you wanted data for just a
single user, it may look something like
"www.myapp.com/users/1" in which case "/users/1"
is the endpoint.
It is important to keep in mind that this
example merely follows convention and is not an
end all be all.
I would check out the Rails guide on routing if
you want more information - http://guides.rubyonrails.org/routing.html