Coriolis force (or more properly, coriolis effect) is the tendency of a moving object to "appear" to deflect one way when the observer is stationary on the surface. In practice for Met purposes, it appears to deflect moving wind to the right in the northern and to the left in the southern hemisphere.
The faster the wind is moving, the more it will deflect ("you can't outrun Coriolis.") Coriolis is proportional to wind speed.
Because this "force" changes from acting left to right, at some point it must be zero. This is when you are neither in the northern nor southern hemisphere - ie, at the Equator. Coriolis is so weak around here it can be ignored for practical purposes. Thinking about it, this also means the Coriolis is stronger the further away from the Equator you are - ie Coriolis is proportional to latitude.