All elements (from a Universal set) NOT in our set.
Example: With a Universal set of {1,2,3,4,5,6}
Then the complement of {5,6} is {1,2,3,4}
Symbol is a little dash in the top-right corner.
Example: A' = {1,2,3,4}
Or a little "C" in the top-right corner.
Example: AC = {1,2,3,4}
Together the set and its complement make the Universal set.
Another Example, for the set below:
• the Universal set is {alex, blair, casey, drew, erin, francis, glen, hunter, ira, jade}
• set S = {alex, casey, drew, hunter}
• the complement of set S is: SC = {blair, erin, francis, glen, ira, jade}