Polarity (according to dictionary.com) means "The possession or manifestation of two opposing attributes, tendencies, or principles." we decided to simplify that down to, a certain object containing two things that are opposite. Just like Sasuke and Sakura. They're personalities aren't very similar (only in a few ways), but that doesn't mean they're not compatible. "Opposites attract" as they say, so we took that into consideration and thought polarity described not only the two in general, but the relationship that they share.