if you are referring to a physical change in a reaction, a physical change is a change that will affect the physical appearance of something without changing the composition (what it is made of)
Explanation:
examples of physical changes are things like changes in texture, change in state (water melting or boiling), change in shape (cutting a piece of paper), change in colour (as long as it is not due to a chemical reaction), change in temperature, etc. All of these changes will not change what the item is made of or what is in it. Some of these changes such as colour, state, temperature can also be caused by a chemical change.
