Thieves, burglars, robbers; call them what you will, but rogues are the kind of people who specialize in taking from the rich and giving to themselves. As a character class, rogues are weakish warriors and able to do a bit of magic. They're especially good in disarming traps, sneaking around stealthily and backstabbing sleeping monsters. A good rogue needs a lot of dexterity and intelligence, at least.
The enemies of The Flash form one of the most distinctive rogues galleries in superhero comic books. Some of the Flash's nemeses, led by Captain Cold, constitute a loose criminal association who refer to themselves as the Rogues, disdaining the use of the term "super-villain" or "super-criminal."