Here is the description:

https://github.com/jax-rs/spec/commit/48d723aaa3d928e4bb4fa3ffcad7ca1fd109563f

Methods of a resource class that are annotated with \Path\ are either sub-resource methods or sub-resource locators. Sub-resource methods handle a HTTP request directly whilst sub-resource locators return an object or class that will handle a HTTP request.