Green’s Dictionary of Slang

(US) a sideburn.

1970		J. Bouton Ball Four 86: Runge [has] been wearing these long, gray sideburns [...] I asked him if he thought he could get by wearing the burns during the season.
1972		B. Rodgers Queens’ Vernacular 38: burnies sideburns.
1998		(con. 1986) G. Pelecanos Sweet Forever 50: Tutt’s flattop was gelled, shaved back and sides, no burns.
2000		Observer Screen 26 Mar. 24: You have to shave those burns, man.