noun
Refers to a person who stays overnight at a lodging, typically paying for accommodation. Slightly formal or written; in casual speech, 泊まっている人 or 宿泊客 is more common.
この旅館は宿泊人に朝食を提供している。
This inn provides breakfast for its lodgers.
宿泊
Please fill in the guest register.
下宿人 specifically refers to a lodger who stays for a longer period, often in a boarding house, while 宿泊人 is more general for any overnight guest.
Compound of 宿泊 (lodging, overnight stay) and 人 (person).