From SKYbrary Wiki
The “force” which pulls an object to the right (clockwise) in the northern hemisphere and to the left (anticlockwise) in the southern hemisphere.
The Coriolis effect is caused by the rotation of the Earth. An object, such as an aircraft, travels in a straight line through space. Because of the rotation of the Earth, the object will appear to veer to the right in the northern hemisphere or back to the left in the southern hemisphere.
Coriolis acts on the air as well as an object flying through it. Air drawn towards an area of low pressure will actually move along the Isobars, the gradient force created by the pressure difference being balanced by the coriolis effect. Thus wind travels clockwise around a area of high pressure in the northern hemisphere and anticlockwise around an area of low pressure. The coriolis effect varies with ground speed (or wind speed) and is greatest at the Poles and zero at the Equator.