The definition of an exception is something that is outside of the rules or outside of the normal expectations.
(noun)An example of an exception is when you are normally supposed to be home by midnight but your parents let you stay out until 1 AM, just for one night.
See exception in Webster's New World College Dictionary
noun
Origin: ME excepcioun < OFr exception < L exceptio
See exception in American Heritage Dictionary 4
noun
Learn more about exception