Matter is anything that takes up space and has mass. The screen in front of you is matter. Buildings are matter. The air you breathe is matter because oxygen atoms have mass.
The three states of matter solid, liquid, and gas are the ways that matter exists. Any atoms that are solid, liquid, or gas are considered matter. Pillows are matter, doorknobs are matter - everything that takes up space and has mass.
What isn't matter?
Outer space beyond the earth's atmosphere doesn't have any atoms of solid,liquid, or gas. The vacuum of space is empty - no matter. Other planets and stars have matter, but the area between planets and stars is empty.