GH2

Stands For
Guitar Hero II(2)

Which means
GH2 is a music/rhythm video game in which you use a guitar-shaped peripheral to play notes as they appear on the screen. It is the second game in the Guitar Hero franchise, hence the name.

Example
Josh: I am getting to be really good at GH2.

Related Acronyms

 * GH
 * GH3
 * GH:WT
 * GH:OT