1. (adj.) Very massive; fat; weighs a lot.
2. (adj.) Serious and intense.
3. (adj.) Hardcore, brutal, raw.
4. (noun) A tough guy.
5. (adj.) Carrying a weapon, most likely a gun.
John: Did you see that guy? He must have weighed 400 pounds?!
Jane: Yeah, I know, he was really heavy.
John: Last night, my mom died.
Steve: Man, that's heavy.
Whitechapel is heavy.
The club was having problems with riff-raff, so they hired a couple heavies to bounce.
The other side came heavy to the fight, so we beat it outta there pretty quick.