It's a virtual force ... one that seems to be there but isn't really there.
When something tries to fly or flow straight, through a rotating neighborhood, it ends up flying or flowing in a curved path, AS IF there were a force acting on it to make it curve. THAT apparent force is the Coriolis force.
It's what makes air, flowing away from high pressure or into low pressure, form the big rotating pressure systems on the rotating Earth.
