It has to take up space. (Have mass)
If there is a 'something' there, then trust me, there is matter in it.
No, because matter is something that takes up spaces, and matter is something that you cant see.
matter
Yes, matter can be something that you can not see. This is because one form of matter is gas, which can not be seen.
Everything that consumes something of matter expels something of matter. So yes, they do.
matter
If something has mass it is matter.
Anti-matter
I know this book is made of matter because it is something around me. Now you think of something that is made of matter.
An idea is not matter (and sometimes does not matter either).
Matter is anything that has mass and takes up space. You can tell if something is matter by observing if it has a physical presence, occupies space, and has weight. If it has these characteristics, then it is considered matter.
Gravity is a main thing that is not matter.