This is a label for the Real Person Slash fanfiction pairing for actors Jensen Ackles and Jared Padalecki, Dean and Sam Winchester from the hit television show "Supernatural." The term J2 comes from the fact that they share the same first initial.
J2 is usually used as an abstract noun, referring to the FICTIONAL romantic relationship between these two actors. Occasionally it is also used as a concrete noun to describe the "couple" themselves.
Fangirl 2: "Oh I know! The way Jensen smiled when Jared told that joke...J2 oughtta just comeout already!"
Stick-in-the-mud: "Guys, c'mon. They aren't gay. They have girlfriends."
Fangirl 1: "Let us dream, wench!"