The phrase "accidental spills" means when something is unintentionally poured or dropped, resulting in a mess or a liquid being spread in an unintended area. Full definition
The breathable fabric helps you keep cool throughout the night while also protecting your mattress from accidental spills and stains. (geekwrapped.com)
There's also a lid - locking system to avoid accidental spills. (recipesfromapantry.com)
The flannel outer cover is hand washable for accidental spills and stains. (geekwrapped.com)