Similar to the rock out hand gesture or corna (devil horns), except you also extend the ring finger, so just the middle finger is down with the thumb. It means you are rocking out harder then usual.

Adj. Something that is expected to have a long lifespan by virtue of having existed for a long time, based on the lindy effect, named for the New York restaurant Lindy's, coined by Albert Goldman and popularized by Nassim Taleb.