1. A demeaning name for those who are born into muggle families and can use magic. These people tend to be disliked by Slytherins due to Slytherins being pure-blooded and believe that only pure bloods should be able to attend Hogwarts.
2. Tend to be intelligent witches and wizards. e.g. Hermione Granger, Lilly Potter
Draco: You filthy mud-blood!
Hermione: WTF U JUST CALL ME!!!
Draco: A filthy, dirty, bluggered, MUD-BLOOD!
Hermione: Taste magic BITCH!! STUPEFY
Justin Flinchfetchly: Hey Hermione. How'd you do on that test?
Hermione: Dude I totally aced that shit! How'd you do?
Hermione: Fuck yea you did mud-blood!!
Justin: O hellz yea mud-blood!!