As an example, if we make a GET request to the URI http://oursite.com/wp-json/ we are returned a JSON response showing what routes are available, and what endpoints are available within each route. /wp-json/ is a route, and when that route receives a GET request then that request is handled by the endpoint which displays what is known as the index for the WordPress REST API. The route wp-json/wp/v2/posts by contrast has a GET endpoint which returns a list of posts, but also a POST endpoint which accepts authenticated requests to create new posts.