Hi YellowGoblin4211,
Thank you for your question!
To make it simple, entropy is a measure of disorder in a system. It is a concept referring to the degree of disorder/unpredictability of a solution/a gas/a system, etc.
It is used in chemistry, mostly thermodynamics, to predict the behaviour of a reaction. The fully understand the concept, notions ranging from Cegep to college are required. You probably won't see entropy in high school.
I hope that helps and feel free to write us again!
Anthony B.