GoldSrc (also known as "Goldsource") is the game engine on which Half-Life (and several games related to it) runs on.
"GoldSrc" was the internal codename for the HL engine during the later stages of its development, when the engine code was forked into a development branch and a stable branch. HL was released with the GoldSrc engine code, and the non-gold "Src" became known officially as Source, which would eventually be the engine used by HL2.
Notable games running on the GoldSrc engine include:
- Half-Life
- Half-Life: Blue Shift
- Half-Life: Opposing Force
- Counter-Strike
- Counter-Strike: Condition Zero
- Team Fortress Classic
- Day of Defeat
- Ricochet
- Deathmatch Classic