The Interface descriptor is a related set of endpoints that present a single feature or function of the device to the host. It basically groups endpoints into a functional group performing a single feature of the device. Endpoint descriptors describe endpoints other than endpoint zero. Endpoint zero is always assumed to be a control endpoint and is configured before any descriptors are even requested. (The Endpoint is memory buffer allocated on the device for sourcing or sinking the data on the USB bus). Finally are the optional String descriptors, which provide human readable information.