What does "one last score" mean? Is it an expression?
Yes, "one last score" is an informal expression. It is most commonly heard in movies/TV shows related to crime or criminal related activity. Usually it is something like a bank robbery or heist in which one gets something through illegal means. "One last score" usually means one last time to perform this particular activity before I stop forever. Ex: This is it man, one last score and I'm done. Ex: This could be it, one last score and we'll have everything we need.