A slang term for 'explain.' Originally used in Joss Whedon's television adaption from the cult classic movie, both respectfully named 'Buffy The Vampire Slayer.' Often used when one is confused on just about anything misunderstood, such as a quote's source or a demon's origin.
Girl: You know, it's not that I hate their ideals, I'm just not a fan of the tacit ethnocentrism in the anti-nightshade movement.
Boy: *tilts his head to the side in confusion* 'Splainey??