A film set is a designated area or locale that provides the backdrop for a movie. It might be entirely fabricated from scratch and constructed on a sound stage to provide the most control possible over what happens on that set. Alternately, a film set may be an actual location such as the Grand Canyon or Eiffel Tower that production has secured for the shoot.
Whether created solely for the film or used for it, the purpose of the film set is to help audiences believe in the world that they are seeing on the screen. No matter if that world is a street in rural America, Mars, or somewhere in between, the film set should sell the authenticity of that world.