The ska stroke, or ska upstroke, is a guitarstrumming technique that is used mostly in the performance of ska, rocksteady, and reggae music. Ska strokes serve as a rhythmic base to a song, and may be doubled by the drums. This style of playing has a dance associated with it, the skank.
Ska strokes are considered a bouncing sound, going up then down in pitch. If a musician is using a general 1 and 2 and 3 and 4 and... on the downbeat, the sound is on the selected guitar chord, and then a ghost note is played on the string on the upbeat. The ghost note is achieved by lifting the fret hand off the fret a few millimeters. However most traditional ska is focused on the upbeat, playing on the downbeat is more closely associated with reggae, where the ska strokes are played much slower as opposed to ska.