Ethernet is a very broad term. I would consider the true definition of Ethernet to be the standards set by the IEEE. So, I would call it neither a topology nor a protocol, but a set of Layer 1 and Layer 2 standards. There are flavors of Ethernet for Category 5 cable, coaxial cable, fiber optic cables and wireless transmissions, among other conduits. With that said, there are several topologies and protocols related to different Ethernet standards.
This was first published in February 2003