(Mostly for taking someone inside somewhere with you. It can theoretically be used for literally taking something inside (like a plant from a balcony), but "reinholen" or "reinbringen" are more idiomatic in that sense. )
(Quite rare overall. ONLY for including an item in some sort of list. Think of a musician deciding to include a certain song in their new album. NOT for including in the sense of "intergrating, welcoming". )