(1) (
Generation 
3)  The third generation of a product, typically hardware rather than software.  See 
3G.
(2) A series of Mac desktops and PowerBook portables from Apple that were based on the PowerPC 750 chip.  Models were introduced in 1997 starting at 233 MHz.  See 
G4.
(3) The third generation of IBM's CMOS-based mainframes (Parallel Enterprise Servers), introduced in 1996.  See 
G4, 
IBM mainframes and 
Parallel Enterprise Server.
(4) (
Group 
3)  See 
fax/modem.