The IEEE 802.3z standard, also known as 1000bt and gigabit ethernet, is an ethernet signaling system that has a theoretical modulation ceiling of roughly 1 billion bits per second, though to due to the CSMA/CD system and protocol overhead, throughput is lowered significantly. 802.3z ethernet usually employs Fiber to the desktop, but can also use Cat-7 copper wire, and even Cat-5 when using the 802.3ab standard (which is still in draft).
The 1000bt moniker can be broken down to the type of baseline signal hardware used: 1000BASE-SX, -LX and -CX. The 802.3z standard is not a system itself, but a series of modification guidelines to the existing 802.3 ethernet standard.