Shin The Gin 2007-01-19 - AFAIK this is a mainboard form factor with a size of 17x17cm, developed by VIA. Boards of this kind are often passively coolable (no fan) and consume less then 40W, inclusive cpu, graphics, tv out, north bridge and south bridge.
This form factor is very popular for case modders and/or friends of small form factors :)
rdt There is also Nano-ITX (120 mm x 120 mm) and Pico-ITX (100mm x 72 mm).