A harp, in lighting terms, is the (usually) brass wire armature, or support, that is mounted to the base of a table lamp just below the lampholder or socket. It loops up around the light bulb(s) to a stud and a finial. In other words, a lamp harp is the thing that holds you lamp shade.
You may have several harps in your house right now.
You may have several harps in your house right now.