"Reggae"(reggay) as a term came into wide use in 1968 or thereabouts, for the contemporary groove being employed in Jamaican popular music. Most of the music in that industry/sphere could be casual labeled as "reggae" of some sort, though other stylistic terms are often preferable for accuracy. Roughly every 2-4 years since the coinage of "reggae," the dominating rhythm of Jamaican music changed, and nowadays -- with producers creating things instead of bands of individual musicians -- one can expect the unexpected.

There is no "the reggae style/beat" per se, therefore, as reggae covers Jamaican popular dance music through the last 50+ years. There was, however, a sort of "export reggae," which reflects what consumers outside Jamaican tended to hear: groups in the style of the later incarnation of Bob Marley and the Wailers. "Reggae beat" seems to have been abstracted from that, and imagined as having a specific groove, though if the groove is at all accurate it only applies to a specific time period. Jamaican music producers seldom go back and do "old" things in that way.There is a sense of continuity and heritage and even "tradition," but it is not articulated by playing the grooves from 1978 as if they were a standardized thing.