Word
Git
Git is the tool that keeps every saved version of your project's files, so you can see what changed and go back to how things were.
Also called: version control, source control
It is the undo history for a whole project, and it is what lets you say "this worked on Tuesday" and actually mean it.
Be clear about what it does not cover. Work you have not committed is not in it, and neither are files it was never told to track. Your database is not in it at all, so it is not a backup of your business data, and a lost order is not something git can undo.
It is also not what makes it safe to let an agent change things. Being able to go back is a seatbelt. Reading the change before you accept it is the brakes.