Pretty much what Weapon and Dre said. Though short for swagger, I consider the full word as a person who also has class/etiquette and can adapt well in classy environments. A guy with baggy jeans, white wifebeater(tank top), black gums, 6 teeth, and can barely speak English (out of stupidity) can have sawg but not swagger. If you put this guy around women with etiquette and some standards, he would freeze up unlike like a shy little nerd in 9th grade.
I've heard swag mean a few things. The most common use I see is in describing free gifts/prizes given away at the door to people who attend special events. Sometimes, however, people use it as an abbreviated form of swagger, speaking about a level of confidence that is visible based on obversvation of the way a person walks and moves.
Swag is also low quality marijuana that is sold cheap as dirt. Language is not universal. Everyone places their own meaning on words. Not everyone in the world speaks English, or do all English speaking people speak the same English. From culture to culture their are variations in meaning and usage. Swag is just one example. F** would be another. F** can be a homosexual person or a cigarette. Why are you so narrow minded?