what is meant by torque in two wheeler?

Answer 1

While the previous answer is very well written, I would like to add that a torque curve is very important as it is torque which accelerates you. Horsepower is what give you a top speed. As indicated they are interrelated.

In an automobile, torque curves are extremely important because of the greater weight they carry. Torque curves are less important on a motorcycle. Nevertheless, if you were driving a racing bike on the street, you would find it extremely irritating to operate at low speeds. This is where a fat torque curve, not just the maximum torque comes into play. Each time you shift, you want the RPM's to fall right onto the center of your torque curve. That's the important of a good transmission and multiple gears. This is why on a car with greater weight, you have to have a fatter torque curve, unless it is an all out racing car.
In contrast, on my old Indian flat head motorcycle, I only have three gears, but the torque curve, while not all that high, is flat as Kansas. It's a lot different when you are younger and you want to go really fast. It takes lots of revs to make serious hp.

Answer 2

Regardless of application, torque is a twisting force. In the context of engines / cars / bikes, you can VERY roughly correlated Torque to engine configuration and displacement. It is, I believe, an average of the twisting force through an engines entire cycle. To get Horsepower (in US / SAE figures), you can use the formula hp = (torque * RPM) / 5252 (roughly). Torque needs to be expressed in lb/ft to work in that formula.

You'll hear religious debate over horsepower and torque. In reality, most people really mean "low RPM horsepower" when they use the term torque. Torque figures and curves are most useful to engine tuners as they decide on tuning compromises.