Having read James May's rather & deliberately confusing explanation of torque i decided to explain in truly simple terms what Torque is in relation to a motorbike engine. Mathematically torque can be written as T = F * r * sin(theta). The above dyno chart is a ZX10R engine i currently have under development the sharp & abrupt drop of is because the governing ECU was set to a lowly 13000 rpm as i am currently working on moving that bulge in the torque curve into a more linear spread. This will be achieved by a manipulation of cylinder bore diameter & crankshaft stroking (increasing the stroke).
Torque is the twisting force that "tends" (is deliberately manipulated) to cause rotation. The point where the object rotates is known as the axis of rotation (crankshaft main bearings).
The way to measure torque and here in the UK we use units of foot pounds is to first determine the lever arm (crankshaft stroke) multiply this by the applied force (the explosion inside the combustion chamber).
The Torque will cause the object (crankshaft) to rotate with an angular acceleration (because it works in a circle) down to rotational equilibrium zero (or bottom dead centre) then it will continue moving with a constant velocity whence the crankshaft inertia becomes a greater measurement than the torque.
Because all rotational motions have an axis of rotation, a torque must be defined as a rotational axis. A torque is a singular measurement of force applied to a point on an object about the axis of rotation which on a crankshaft is 90 degrees.