Ethernet cable is one type of network cable. Fiber optic is another different type of network cable.
are different grades of ethernet cable.
Cat6 is the ethernet cable standard used for gigabit networking (1000Mbs). Cat5 is the standard for 100Mbs. Cat6 is backward compatable, so it will work just fine in the place of Cat 5 cable. I recommend Cat6 cable even if you don't need it, so long as there isn't a big difference in cost when you purchase it.