A main refers to when a video game has multiple characters/weapons/profile to choose from and a gamer has chosen a particular character he specializes with, usually for online play.Mains are chosen usually as their game play characteristics caters to the style of play of the gamer. Although some mains are chose out of media popularity of the character despite their inherit weaknesses (ex. Cloud Strife in Dissidia, Link in Soul Calibur, etc.).Noobs often main characters which they can spam (repeatedly use the same move over and over with relative success in gameplay)
1. the most important
2. a favorite girlfriend or boyfriend
3. a best friend, usually a dude, as in "my main man".
4. ebonics for "man"
5. main vein, the vein used to inject heroin, see also main lining
Example: 1. "if you're going to snort it, you might as well pop it, and if you're going to shoot it, you might as well main it" (from basketball diaries by jim carroll)
2. "that's my main girl"