For the user experimentation page, please see Memory Alpha:Sandbox.
A sand box or litter box was a container used by cats for urination and defecation.
In 2370, Data asked Worf to cat-sit Spot, saying that he must provide the cat with a sand box. (TNG: "Phantasms")
After the stock exchange on Targalus IX had been turned into an animal hospital as part of their conversion to a cashless society, the old briefcases were being used as litter boxes. (LD: "Shades of Green")