The term 'Forerunner of Reggae' can be summarized by the crossword solution SKA, which is a three-letter word. SKA is a genre of music that originated in Jamaica in the late 1950s and is considered to be the precursor to reggae. It is characterized by a fast tempo, offbeat guitar skanks, and a strong emphasis on the offbeat. SKA has been influential in the development of other genres such as rocksteady, dub, and two-tone.