What is torque?
Torque is the rotational analogue of force. It is the equivalent of force which makes a body rotate about some axis.
As you may see, it's the equivalent of force which makes the nut rotate about it's axis.
Torque is a vector, i.e. it has a direction associated with it. It is the cross product of vectors
Image : hyperphysics.phy-astr.gsu.edu