backer board

Noun

backerboard (countable and uncountable, plural backerboards)

1. Boards used as underlayment for tile, plaster, or other materials.
   • A tile setter mounts colorful American-Olean ceramic tile on a new gypsum backerboard in a motel bathroom...1962, “A building product for any need”, in National Gypsum Company Annual Report, page 4
2. A sacrificial board placed behind or under a board being drilled or sawn, so as to prevent blowouts. (Usually scrap ends reused for such purpose.)
3. Sheets of cardboard or similar material used to preserve or display books, magazines, art prints, etc.
   • Campos likes this shop not only because it's just a few blocks from his Glendale home but because of the little extras that Brown throws in, like wrapping each comic book with a backer board in a plastic protective sleeve.2006 May 6, Angela Rabago-Mussi, “Drawn to comics gets your spidey senses tingling”, in Arizona Republic, Phoenix, Arizona, page 10