头衔 (tóu xián) is a broad noun for any official or honorary title or rank, like 'professor' or 'president'. It contrasts with 职称 (zhí chēng), which is limited to formal professional rankings in a career system, and 称号 (chēng hào), which is a specific honorary designation (e.g., 'Hero'). 称呼 (chēng hu) is the form of address (e.g., 'Mr.'), not the title itself.