Torque is the amount of twisting or turning that a force exerts about a point. Torque may be considered work done in rotation. The unit is the Newtonmetre. Symbol: Nm.

For example, when you twist something, you are exerting a torque on it.

The imperial way of measuring torque is pounds feet (lb/ft) or pounds force feet (lbf/feet).
There are many different units of measurement for torque, but they will always mention force (Newtons, Kilogrammes force, pounds force) and distance (metres, feet inches).
It is simplest and best to use SI, but you will come across many different types of units.