I heard the movie The Hangover is unscripted. Is this tru and what does it mean?

I don't think "The Hangover" was unscripted, but anything unscripted just means that the actors are given a general idea of each scene in the movie or TV show and they improvise the words and actions. It's kinda like telling someone to make a peanut er and jelly sandwich but letting them decide if they want to put the jelly on first or the peanut er and all the other combinations you can come up with. They are not told exactly what to do and have the option to add their own comedy. See "Curb your enthusiasm" by Larry David (maker of Seinfeld). The entire show is unscripted.