"Roots, rock, reggae" is a song from the second Bob Marley & The Wailers album, Rastaman Vibration. The title refers to what has influenced reggae. The roots are the Rastafari Zion: Africa. The rock is jamaican rocksteady and ska musical genres, both of these styles are also referenced in the simple beat and rhythm underscoring the song.
Over time, reference to the song has dropped the commas, so that one might think the song was referring to "roots reggae" and "Rock and roll". Dropping of the commas was used in a documentary from 1977 of the same name, which covered the history of reggae, interviewing Marley, Dennis Brown and Jimmy Cliff. There is a "Roots Rock Reggae Festival", usually headlined by several of Bob Marley's children, which incorporates rock acts and reggae acts. Begun in 2004 and originally sponsored by High Times and Phillip Morris, it runs sporadically on the east and west coast of the US.
The song itself is 'reggae lite', filtered down for mass appeal. The lyrics hint at this with the line: "Play I on the R&B, want all my people to see: / We bubblin' on the Top 100, just like a mighty dread!". With the success of their first album, Marley was quite aware they wanted to continue with popularity. Youtube has a video of Bob Marley & The Wailers performing it for Top of the Pops on an orange sherbert coloured set. Although there is a rich history and a wealth of fantastic Reggae music, when most people think of the roots that rocked reggae, they are thinking of a Bob Marley song.