What is the meaning of Backerboard?

A board used behind or under other material, often as support.

1. Boards used as underlayment for tile, plaster, or other materials.
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.

Boards used as underlayment for tile, plaster, or other materials.

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.)

Sheets of cardboard or similar material used to preserve or display books, magazines, art prints, etc.

Source: wiktionary.org