From QWiki

In QuakeWorld terminology, a cam is a person connected to a server as spectator via a Qizmo proxy. This allows other spectators to connect to the same proxy and spectate the cam, rather than being connected to the actual server the game is played on.

Due to bandwidth limitations, most QuakeWorld servers usually only have 2-8 spectator slots. However, in order to enable the mass viewing of games with a large public interest, these spectator slots are often reserved for cams in big games. Qizmo proxies usually have 16-64 slots. So if 4 cams, each on a Qizmo proxy with 32 slots, are connected to the server the game is played on, the game can thus be spectated by (4*32=) 128 people rather than 4.

This method of mass spectating, however, is now replaced by QTV which brings the huge benefit of streaming the multi view demo (MVD) of the game, thus allowing all spectators to spec whoever player they want rather than being restricted to spectating the player currently selected by the person serving as cam.

QuakeWorld terminology
Game stuff
Quad | Ring/Eyes | Pent
GA | YA | RA | Mega
Axe | SG/Boomstick | SSG | NG | SNG | GL | RL | LG/Shaft
Binds | Bunnyhop | CFG | Demo | Duel | FFA | Frag | Rocket Jump | GLRJ | rpickup | pickup
Cam | Flood | +forward | BG | CS | GG | HPW | LPB | MGT | MST | Kenya | Rapecloset | TB3 | Stomp | BO3 | BO5 | Div1 delay | kpickup