庸俗 (yōngsú) describes something that is vulgar, tacky, or in poor taste — lacking refinement or class, often in style, speech, or behavior. It is stronger and more judgmental than 俗 (sú, 'common, coarse'), which can just mean 'popular' or 'earthly'; 庸俗 always implies disapproval. Unlike 难听 (nán tīng, 'offensive to the ear') or 粗 (cū, 'rude, rough'), 庸俗 focuses on tastelessness and lowbrow quality rather than harshness or coarseness.