Reverse Engineering occurs when you take a finished product and working backwards to determine how it was constructed or engineered. By breaking a product or piece of software down into its component parts you can extract a good deal of information about the product. This strategy is very common in forensic investigations to determine the root-cause of how a breach occurred. It is also often used by nation states to steal intellectual property from other countries rather than having to create a novel product or the IP to begin with.
Related Term: Reverse Intent