What is the meaning of the idiom 'to fight fire with fire'?

This expression metaphorically means to respond to a situation or threat in kind - for example, if they are going to fight dirty so will we, or if that company is going to slander us in their ads, we will do the same. It means to use the same weapons, techniques or strategies used by your opponent, competition or foe.

It also has a literal meaning. In fighting forest fires, fire itself is often used to stop the renegade fire from spreading. This is done by burning a wide section of forest or field ahead of the fire, so that when it reaches that point it will have nothing to burn and will fizzle out.