Matter is any substance that can occupy physical space. More presicely saying anything that physically exist in this world,
say for example Air is matter,water is a matter,
Matter exist mainly in three forms liquid,
Gas,solid and under special conditions they may exist as plasma,foam Bose Einstein condensate
Not all matters are visible to the human eye
and can be felt or touched by us
Atoms are matters but we can't neither see it or touch it,
protons neutrons electrons these three combine to form atoms and they are "matters" but we can't feel them or see them
So simply saying a matter is anything that can occupy physical space. They are found in 6 states