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.
Originally made of wood, the cat box today is most basically represented by a plastic tray with outwardly-sloped sides several inches high. More elaborate models are enclosed, looking similar to pet carrying cages with open doorways, providing some allegedly-desired privacy to the pet, and better odor control, as well as keeping the litter out of sight. To facilitate emptying the litter box, plastic liners may be used.
Simpler designs exist, for example, some require the owner to manually shake the clumps into an easy-to-remove tray, designed very clean. Another variant has an enclosed sphere which rotates as it sifts out the clumps and deposits them in a drawer below the sphere. A new method involves incorporating sifting functionality within a sifting litter liner.
A potential problem is that cat feces can contain a parasite, toxoplasma gondii, that has been linked to the death of marine mammals, including sea otters, whales and porpoises. The parasite can survive conventional sewage treatment and can make it to the sea where it can cause fatal infections in sea mammals. Cats generally pick up this parasite from eating prey which is already dead; therefore, cats who have spent their lives exclusively indoors are not likely to carry it.