Half-Life: Source is a digitally remastered version of Half-Life, enhanced via Source technology to include physics simulation, enhanced effects, and more. It was released by Valve Corporation on June 1, 2004. Following the release of the Half-Life 25th anniversary update, it was delisted from Steam, and is now bundled for free with Half-Life Deathmatch: Source.
The game has three different engine versions to choose for speedrunning. Make sure you know the differences.
The c1, c2, etc. prefixes stand for Chapter 1, Chapter 2, and so on respectively. t0 stands for Training.
There is a total of 103 maps, 6 of which are part of the Hazard Course, and 24 are either skippable or ignored in speedruns.