Valve have released the latest small update to Team Fortress 2. Following on from the update released at the start of May, it's another that pulls in some community-provided fixes thanks to the source code being available as part of the Source SDK update.
Fair enough, then a more apt statement would be a permissive non-commercial license with media assets injected from the base game (alla GMOD)
I’ve heard the term source available be used, though not sure how popular it is.