Square was a slang term used in 1955 to describe someone who was untrendy or 'not with it'.
The term appeared on the poster for the Enchantment Under the Sea dance seen by Dr. Emmett Brown and Marty McFly at Hill Valley High School on November 12, which urged students to “Be There... or Be Square!”
In 1986G, the Jennifer Parker of this timeline, a punk girl who regularly broke the rules, dumped an alternate version of Marty because he wasn't good at playing guitar and followed the rules — making him a 'square'.
- Back to the Future
- Back to the Future: The Game
- Back to the Future (IDW Publishing)