A family (like a door or window) that must be placed on and cuts into another element - the "host" - rather than standing on its own in free space. A door family is host-based on a wall (delete the wall and the door goes with it), while a face-based family can attach to any suitable surface, and a stand-alone family - like most furniture - needs no host at all. Choosing the right hosting behavior when building a custom family in the Family Editor determines how forgiving it is to place and move later.