The phrase "baby poo" refers to the poop or bowel movements of a baby. It is a way to talk about or describe the waste that comes out of a baby's diaper. Full definition
That includes lessons learned the hard way (there's a tipping point at which a onesie covered in baby poo needs to be cut away and discarded, not pulled off, cleaned, and saved, for example) as well as use of an arsenal of baby care products that made caring for our son that much easier. (businessinsider.com)
As will the risk of baby poo leaking onto baby vests / onesies (yellow and bitty for breastfed babies, sorry to be gross). (charlottekeating.com)
If baby's poo is very runny, explosive and a larger amount than normal, you're most likely seeing diarrhoea. (bounty.com)