娘儿 is a colloquial term for 'mother' used in limited contexts, primarily in northern Chinese dialects or older literary works. It's not the standard word for mother (妈妈 is far more common) and often carries a folksy or rustic tone. You'll most often encounter it in set phrases or fixed expressions like 娘儿俩 ('mother and child/children'), where it refers to a mother and her offspring together. Don't use 娘儿 in everyday conversation — it can sound outdated or overly regional.