The Free On-line Dictionary of Computing (30 December 2018):

reverse engineering

    The process of analysing an existing
   system to identify its components and their interrelationships and
   create representations of the system in another form or at a
   higher level of abstraction.  Reverse engineering is usually
   undertaken in order to redesign the system for better
   maintainability or to produce a copy of a system without access to
   the design from which it was originally produced.

   For example, one might take the executable code of a computer
   program, run it to study how it behaved with different inputs and
   then attempt to write a program which behaved identically (or
   better).  An integrated circuit might also be reverse engineered
   by an unscrupulous company wishing to make unlicensed copies of a
   popular chip.

   (1995-10-06)