So in the strictest sense, "IP over Ethernet" is exactly what it sounds like, it's the encapsulation of IP packets (datagrams, formally) in standard ethernet frames. For much of the networking universe this is just "normal" IP as so much of the transport has migrated to Ethernet nowadays. Somewhat more specifically speaking, IPoE is often used in comparison to PPPoE when discussing how services such as residential broadband are delivered to the end user. This can be a little confusing as PPPoE would more accurately be described as "IP packets encapsulated in PPP, which is in turn encapsulated in Ethernet"... but it's just broadly known as "PPPoE".
The use of either "PPPoE" or "IPoE" in the context of residential broadband also almost always implies other components of the service delivery system, such as address allocation, authentication, accounting, etc. Authentication is normally a RADIUS server or sometimes Diameter. The exact rules on how authentication is performed and what devices can/can't connect are usually set up by the specific service provider. Broadly speaking, "IPoE" is more common in cable access networks, and "PPPoE" is more common in DSL and dialup access networks: although this is by no means cast in stone.
I found the document below to be relatively useful: