what is reverse engeneering?

Answer 1

Say you have a battery powered toothbrush. Looking at it you see it can be turned on and off. It has a waterproof case. It moves however it happens to move. What is inside is hidden from you, but you can make reasonable guesses about it. Therefore, you can build your own without knowing what is inside. That is reverse engineering. Figuring out how to build something based on what it does and how it interfaces with the world.

Answer 2

It deals with discovering how a program, function or feature works whose source code is not available, to the point of being able to modify that code or generate its own code that fulfills the same functions

Answer 3

essentially a long and extensive process of research about something to get a level of understanding, of its inner working, comparable to that of its creator(s).