Disambiguation:

Git for Windows - The application stack that contains the Git Bash application
Git Bash - The application that launches a Git-ready Bash shell on Windows, that is installed by Git for Windows
msysGit - The infrastructure needed by Git Bash, a "minimal system", sitting mostly atop minGW

All three are roughly equal, but now that I've been teaching for a bit, I see why everybody uses "Git Bash".  It's the name of the executable you double-click on when you want to start Bash in Windows.  This trumps any greater naming efforts :)