茅坑 is a colloquial term for a simple, often outdoor latrine pit — the kind you'd find in rural areas or older public facilities. It's a concrete noun, but the word carries a rustic or crude connotation that 'latrine' alone may not convey; it's not used for modern flush toilets. You'll also hear it in the vulgar idiom 占着茅坑不拉屎 ('to squat on the toilet without shitting' — meaning to hold a position without doing the work).