The Coriolis effect is an inertial force that deflects every freely moving body on Earth: to the right in the Northern Hemisphere and to the left in the Southern. It is not a real force but a consequence of the rotating reference frame.
Impact on weather
It is responsible for trade winds blowing from the northeast (not due north), for cyclones spinning anticlockwise in the Northern Hemisphere and clockwise in the Southern, and for the existence of the geostrophic wind. Without the Coriolis effect, wind would blow straight from high to low pressure and lows and highs as we know them would not exist.