The term is “flatback”.
What this refers to is the smooth “flat” finish for the non-adhesive side of the tape. The most popular paper tape is masking tape, and it has a “creped” textured finish as opposed to being smooth.
Being “flatback” means that 724 paper tape has a smooth surface for writing or printing. This is one of the features that makes it so compatible with the Sharpie Marker every sound or lighting tech has in his pocket.