Excreta is a laboratory and public-health word for the waste people and animals send out of the body. It usually covers more than solid waste: urine and faeces, and sometimes other discharged matter. You will see it in biology, farming, and hygiene writing, almost never in chat. It comes from Latin already in a plural shape, and English has never quite settled. Careful science writing may treat it as plural — “the excreta are collected” — though many writers use it as a mass of stuff: “excreta is collected.” Both happen. Though actually, students often treat it as a fancy twin of excrement. The tidy difference is that excrement usually points at faeces, while excreta is the broader bin the lab uses.