The canonicity of pissing and shitting refers to a thought experiment surrounding the likelihood of characters from any given fictional world produce urine and feces. If one of the aforementioned byproducts can be proven to exist within a particular world, it is assumed that the other does as well, unless there is strong evidence of the contrary.
This is a line of thought ocellaroid often walks as a result of observing a lot of art that features characters consuming large quantities of food and drink. Many such works do not contain any mention of urination or defecation, leading one to wonder if these phenomena occur within the world of the story at all.
A fictional world is deemed to have canon piss and shit if one or more of the following criteria are met: