Cunnilingus is a formal, almost medical word for using the mouth — the lips and tongue — on a woman's outer sex organs, to give sexual pleasure. It names the act, not a person. In ordinary talk, people usually do not use this word; they say something shorter, or they do not name it at all. You will see it in sex education, in health texts, and in legal or medical writing. It comes from Latin: the first part is an old word for the female sex organs, and the second part is "licking". Though actually, in early Latin the word named a person who did this, and only later — and not fully at first, even in the early 1900s — did it settle as the name of the practice. English now treats it as the act. The word itself is not slang, but the topic is private, so tone still matters.

舔陰（口交的一種，針對女性）