As the others have said, it means "out of". Forget about using "outta" and just use "out of" - there's nothing wrong with speaking English properly.

As everyone else has said: the sound 'outta' is just what we hear when someone speaking fast or carelessly says 'out of.' Be prepared to understand it when you hear it? Certainly Say it? Probably not Write it? Definitely not And I just want to add that Peachey's comment : 'THERE'S NOTHING WRONG WITH SPEAKING ENGLISH PROPERLY' is the sanest thing I have read in a long time in these pages. So true. It should be written across the italki masthead. Every time someone asks about gonna, gotta, wassup, and 'I wanna learn slang' we should refer them to these words of wisdom.

"outta" is a way of saying "out of" and therefore also a way to spell it. There's no need to use this 'word' unless you are trying to behave like a certain person or act a certain way, but it is useful to be able to understand in case you do see/hear it. There's nothing wrong with using proper English, but there's also nothing wrong with using whatever words (or non-words) you want. Just make sure you understand how other people might view your use of language. Similarly, there's no reason to use: IMO (instead of "in my opinion") LOL (instead of "haha") g2g, ttyl (instead of "got to go, talk to you later") ur (instead of "your" or "you're") but they're not all viewed in the same way.

"Outta" is a gramatically-incorrect spelling of "out of". For example: "Let's get outta here!" "I'm taking it outta your paycheck." I would advise against using it in writting, as in reality it isn't a word, but in speech it is simply a mix of the two words, like "gonna" (going to).

Abbreviation of OUT OF in American informal English.