Excrement is the solid waste that leaves the body through the bowel — what children call poo. It is a stiff, careful word: doctors, biologists, and people trying to be polite-in-a-formal-way use it. In ordinary talk, speakers usually say poo, or poop in more American and childish speech. Medical notes often say faeces. Though actually, “excrement” can sound either very clean or a little comic, because it is so starched. There is also an old, almost dead sense from a different Latin verb meaning “grow out,” where excrement meant something that grows from the body, like hair or nails. You can ignore that sense unless you are in a very old book. This is not the rude word, and it is not a casual insult; it is the science-and-formality coat for a bathroom fact.