A litter box, sometimes called a "sandbox", "sand box", "litter tray", "litter pan", "catbox", or "cat box" is an indoor feces and urine disposal box for cats (as well as rabbits and other pets that naturally or through training will make use of such a repository) that are permitted free roam of a home but who cannot or do not always go outside to relieve themselves.

In the wild, cats naturally excrete in soft or sandy soil, for easy burial. To simulate this instinctively desired type of site and stimulate the natural inclination to hide the excretions, a litter box's bottom is filled typically with an inch or more of litter box filler (frequently called "cat litter" or "kitty litter", though this is a back-formation - the "litter" in "litter box" is actually a euphemism for fecal matter, not for the substrate that pet owners line the box with). Litter box filler is a loose, granular material (most often made of clay, often formulated to clump solidly, though recycled paper "pellet" and silicon based "crystal" variants are also popular options), that absorbs moisture and which meets a cat's instinctive desire to use an easily-dug material. It is best to place the litter box on a mat or some newspaper, as the cat will inevitably kick some litter over the edge of the tray when using it and track some of it out of the box, on their paws.