What are "minus frames"?

I've already done a search, but I see people saying + so many frames and - so many frames. What does all this mean? Sorry, I did a search and couldn't find any info. Little help?

Spike

 

Check the quick guide I did:

http://virtuafighter.com/versuscity/showflat.php?Cat=&Board=training&Number=84637&page=1&view=collapsed&sb=5&o=&fpart=1

It refers to how far ahead your or your opponent is in advantage/disadvantage ie if I'm playing you and I hit you say with a move that leads me +2 frames on hit then your are -2 frames on hit. A jab say comes out in 12 frames but because I'm 2 ahead of you I only need 10 for it to come out yeah?