Torque is a force that tends to rotate or turn things. Informally, torque can be thought of as "rotational force". You generate a torque any time you apply a force using a wrench.
Torque is important in the design of machines such as engines. The measurement of torque is also important in automotive engineering, being concerned with the transmission of power from the engine through the drive train to the wheels of a vehicle. Torque (and power output) can be measured with a dynamometer.