Great question. The city where you live has a building and safety department that is responsible to insure that all buildings "meet" the minimum of building standards to provide safety. If you do any work on your home, you should first purchase "building permits" from the city. An inspector from the city will come to your home after the work is complete to inspect this work.
When you "meet code" you are making sure the work done on your home meets the "minimum" standards. These codes are for your protection. Unpermitted work is poor work.