Matter is anything that takes up space. All matter has a measure of volume and mass. From those two fundamental properties, the density (mass / volume) can be calculated, and if the force of gravity is known, the weight of matter (weight = gravity * mass) can be known.
All matter is subject to phase changes, whereby the addition or subtraction of energy causes the matter to change its physical state from one phase to another. The three standard phases of matter found on Earth are solid, liquid and gas.
Solids alone have a fixed shape and volume, with molecules that vibrate in place. Liquids have a fixed volume, but do not have a fixed shape; their molecules still touch but move around each other, Gases have neither a fixed shape nor volume; their molecules seperate from each other and will expand to fill the container in which the gas is stored.
Gases alone are compressible; solids and liquids are not.