1)To hurl everything out of your stomach and then some... meaning that burning fluid called bile. Something a lot of people really don't like doing in whatever circumstance.
2) The stuff that actually comes out of you when barfing.
Girl 1: Dude, did you see that girl vomit during science class? The trashcan was right in front of me!
A person who does not consume alcohol, do drugs of any kind (even marijuana), smoke cigarettes, etc. They live a lifestyle and have a mentality of pride in their and other's courage not to do these mostly harmful activities.
Typically, kids who chose to be straight edge are associated with the "hardcore scene" and X or XXX symbols. However, many people who chose the straight edge lifestyle do not write X's on their hands and show it off, or any of the annoying crap associated with straight edge.
Me: I'm so glad we're straight edge.
Ethan: Me too, I think drugs and all of that stuff is fucking stupid to do. Getting wasted for a good time is lame.
Me: Yep. But let's not do that annoying XXX shit.
Ethan: Okay, cool.