Ethernet is the collective name for a group of standards defining local area networks. These standards cover cabling and the structure of data sent over those cables, as well as the hardware that connects the cables.
Ethernet works on many different types of network architecturesstar, bus, mesh, whatever. The standard goes into great detail specifying cable types, data format, and procedures for transferring that data through those cables. Because of this, Ethernet comes in several flavors based on the type of hardware and network architecture you've chosen to use.