1 definition by UniversalPLague

Top Definition

OP4 stands for Opposing Force, the first and most popular expansion pack for Half-Life.

EdrianShepperdBoi - Wen is OP42 comeing out? Coz I kno thet the gman kept Shepperd coz he riminded him of him lol.

by UniversalPLague March 30, 2005