Torque is a measure of twisting power, and is used to calculate horsepower. Torque is typically (especially when referring to torque levels in vehicles and engines) measured in foot-pounds, which is a measurement of the amount of force applied over the distance of a foot.
Engines that don't run at a high RPM tend to have a higher torque number than horsepower, and since trucks and other heavy-work vehicles have low-RPM engines, they are usually marketed with torque numbers rather than horsepower.
Introduction to Torque
In this video by Khan Academy, Sal Khan explains the physics fundamentals of torque.