In physics, mass (from Ancient Greek: µ??a) commonly refers to any of three properties of matter, which have been shown experimentally to be equivalent: inertial mass, active gravitational mass and passive gravitational mass.

In everyday usage, mass is often taken to mean weight, but in scientific use, they refer to different properties.

Mass is the amount of matter or substances in a body.

Mass is a scalar quantity

SL unit for mass is kilogram

The mass of an object can be measured using:

here is a video further explaining what is mass

http://www.youtube.com/watch?v=uvy4nWh0KwE