Redefine means to "give new meaning to." A really fantastic song might redefine what rock and roll can mean to people. A great muffin might redefine the idea of what a muffin can be.
Technically, redefine means to define again or differently––to give a new meaning. As a basketball player, Michael Jordan redefined the jump shot––it became something much more common and much more aggressively taken. By turning the packaging design of Campbell's soup into paintings, Andy Warhol redefined art.