Actually, I'm told that BNC stands for "Bayonet N Connector." If you inspect
an "N" connector, you will see that the inside closely resembles a BNC but it
has a huge external screw on ring to secure it. The BNC uses a much smaller
bayonet ring to secure it.

The large housing of the N connector makes it suitable for use with large
cables like 5/8" antenna transmission line. The much smaller BNC is limited to
smaller cables like RG-59, which makes it a great choice for video.