The term 'MC' stands for Master of Ceremony.....in Laymans terms this means they are supposed to host the night.
This should involve introducing the DJ and Introducing the last tune etc. The main job is to keep the energy and vibe up in the venue by interacting with the crowd.
They originated from the very start where detroit house followed on to hardcore, then jungle and now into Drum and Bass. They are a huge part of the scene although we should never forget it's ALL ABOUT THE MUSIC at the end of the day. There is some absolute cock's out there as far as MC's go who talk rubbish and don't do anything for the scene - However...I think hearing a DJ playing out with a good MC over his set sounds wicked! Andy C and GQ for example....GQ does all of the above and knows when to shut up and when to do his job.....an absolute veteran in the game!
Some MC's do need to be shot though! LOL