A polite term for 'stay' or 'overnight stay' — staying at an inn or someone's house for one or more nights.
今週末は友達の家にお泊まりする予定です。
I'm planning to stay overnight at my friend's place this weekend.
温泉で一泊お泊まりして、ゆっくり休んだ。
I stayed one night at the hot spring and had a good rest.
出張中はホテルにお泊まりになってください。
Please stay at the hotel while on your business trip.