Super size (probably a trademark) is an option on meals at McDonald's restaurants where the 6 ounce Large fries are replaced with a 7 ounce container of fries and the 32 ounce drink is replaced with a 42 ounce drink. This trend is present in many fast food restaurants, usually under a different name (Biggie Size, Upgrade, etc.).
On March 3 2004 McDonald's announced that it was discontinuing the super size options on their US menus (Canadian menus got away with a renaming: large size). This decision was made to combat recent bad publicity and numerous obesity lawsuits. Also cited as a reason was a drive to simplify their menu that has been happening since 2002.