backing paper; backing sheet
Paper used as a backing or lining, often in crafts, framing, or stationery.
The backing paper of the picture frame was torn.
paper used on one side; reverse side of single-sided printed paper
Refers to paper that has been printed or used on one side, with the blank reverse side available for reuse. Common in office and eco-friendly contexts.
I use the back of used paper for memos.
Compound of 裏 (ura, 'back, reverse') and 紙 (kami, 'paper'), with rendaku voicing giving がみ. The word transparently means 'back paper'.