Lets talk about Reverse Engineering briefly, because this is also important thing to know when you want to become an expert hacker.
Reverse Engineering is an activity to discover the material how a something is made, how something is works and what is its purpose. In the other word, discovering the technological principles of something by analizing its structure, function and operation. Usually the thing that want to be reverse engineered is taken apart from its original form then analyze each part one by one throughly.