soaker pad

Meanings

1. A waterproof mattress topper, especially one intended for urine (i.e. unpotty-trained or incontinence); a bed protector.
2. Synonym of meat pad (“an absorbent pad placed underneath raw meat in order to absorb excess moisture and fluids (like blood) so as to prevent the buildup of harmful bacteria”).
3. A diaper insert, especially a booster pad.

Etymology

From soaker + pad, due to the absorbent pad's purpose of soaking up liquid.