What is the application. Does the definition, in a textbook, explain it for you.
Shahab Mirza:, remember the rules of this forum, you have to show your work. What you've asked for is a definition, it has no calculation for us to help you with -- either you read it in your textbook, or notes, or you don't. We can't hint, or help you read. We can only do it for you.
You've mentioned already, that your MCAT's are due. But plaese remember, according to our forum rules, you have to start your work early enough.