what is momentum of light tell me about it as i did not know about it

The word "mass" has been used in two different ways in physics. One was the way Einstein used it in E=mc2, where mass is really just the same thing as energy (E) but measured in different units. This is the same "m" that you multiply velocity by to find momentum (p), and thus is sometimes called the inertial mass. It's also the mass that provides the source of gravitational effects. Light has this "m" because it has energy.