A muggle is a non-wizard. Their often hated by Wizards and Witches because they can't produce Magic. Gellert Grindelwald said that he wanted to come out of hiding, and persue the Witches and Wizards to become the top, and for muggles to serve at their feet, with the quote. "Magic is Might!"
Muggles wear clothes that look often as most wizards call it, "Weird."
They hold normal jobs, such as accountants, lawyers, doctors, etc. Some wizards have succesfully been able to hide themselves as a muggle such as Kingsley Shackelbolt.