Okay, there could be a lot of meanings for this word so you'll have to tell us which one you wanted to know..
From the dictionary, it means "bundle" or a "prize" like, "A SWAG of money and gold." This word, (As far as I can recall) is most commonly used for anything that is stolen.
On the other hand, if you are implying for the colloquial term (slang), it means STYLE.
Example: "Girl, you got some swag! Love it!"