A call-in is a radio or television programme where people at home telephone the studio to talk — to give an opinion, ask a question, request a song, or tell what happened to them. The host puts the caller on air. Though actually, English also uses it as an adjective: a call-in show, a call-in hour. In American English, call-in can also mean the act of phoning that show. The hyphen is usual on the noun and the adjective; the verb is two words, to call in. It is everyday media language, a little informal, very familiar wherever late-night radio lets strangers argue with the host.