define means to say exactly what something means or describe exactly what something is like.

The meaning of define is to describe something correctly and thoroughly, and to say what standarts, features, characteristics, qualities etc it has that make it different from other things. Also, there is another simple meaning that is to explain exactly the meaning of a particular word or idea... Regards !!!

Hello Nidal, Here it means to state and express precisely that meaning using your own words.

To put it simply, it means that you must be able to explain the thing that you understand. For example, to show that you fully understand computers, you must be able to explain what computer is, what it does, what it looks like, etc - thereby "defining" a computer.