俗 (sú) is a broad adjective meaning 'popular, common' (often with a negative connotation of being lowbrow) or 'vulgar, coarse'. It contrasts with 通俗 (tōng sú), which is neutral and means 'popular, easy to understand' (like 通俗歌曲 'pop song'), and with 庸俗 (yōng sú), which is strongly negative and means 'tacky, tawdry' (like 庸俗趣味 'vulgar taste'). 俗 can also mean 'secular' (opposite of 雅 yǎ 'refined').