What is Centrifugal Force?

Centrifugal force is the force that is equivalent in magnitude but opposite in direction to the centripetal force, which is the force directed toward the center of a rotating or revolving mass.

Think of it this way. Let's say you have a yo-yo and let it unwind. Then you begin swinging it around your head in a circle parallel to the ground. The force that keeps the yo-yo in its circular path is the centripetal force. Without it, the yo-yo would not continue in its circular path but would fly off in a straight line, which it is inclined to do. The tension in the string, the force that makes the string taut, is the centrifugal force.