What is the difference with HL and HL source

Half life is the original game that was created by Valve that made them so rich and big. Half life: Source is the exact same game, but in the Source Engine. The Source Engine is the game engine that games like Team Fortress 2, Half life 2, and Portal use. Half life: Source is also said to have slightly upgraded graphics. It can also be used as content in mods or in Garry's mod.