Is ethernet a protocol or cable? How it is different from Cat-5 cables? I'm very confused when I hear the term 'ethernet' for a protocol and cables.
A collection of protocols, detailing the physical and logical data transmission. There are details on wikipedia: http://en.wikipedia.org/wiki/Ethernet
The cable is described as an "Ethernet" cable because it can carry Ethernet traffic, but it isn't specifically just for Ethernet. Category 5 cable is a specific set of standards for unshielded twisted pair cable; see http://en.wikipedia.org/wiki/Cat-5
There are cables specifically designed for Ethernet
and there are Ethernet standards that specify cables
There are specifications for testing and certifying terminated Ethernet cables and fixed Ethernet wiring
There are Ethernet standards that describe the electrical signals carried on those cables, how data is to be encoded and arranged, and how those signals and data are to be processed by computer and network-interface firmware or software.