What it is chemistry?

Chemistry is the science of matter and its changes that occur. Everything in our universe is made up of matter and it has to have mass and take up space to be considered this.

If you are requesting a definition of chemistry, here it is per use of google--

The branch of science that deals with the identification of the substances of which matter is composed; the investigation of their properties and the ways in which they interact, combine, and change; and the use of these processes to form new substances.