the musician's best fake friend

Being a music lover is something that daughter and I have in common. We both really love to watch concerts and gigs of my favorite bands, both local and foreign. Too bad, we can only get to watch these things on TV and in youtube. At one point, though, I was wondering how these musicians are able to play all the songs flawlessly in every performance. Not that it was really a big deal for me then to be able to find that out but a friend of mine who happens to be a member of a show band has once shared to me their secret. Aside from regular rehearsals with the members, they have got to have one thing to complete their music paraphernalia - the fake book! I was told this has been what's keeping their trade alive in every gig. Truly, musicians have found a real friend from what is called a fake book. :-)