A lodger is someone who rents a room in another person's house or apartment. Unlike a tenant who rents an entire apartment or house, a lodger typically lives in just one room while sharing common spaces like the kitchen and bathroom with the homeowner or other residents.

In many classic novels, characters take in lodgers to earn extra money. A widow might rent out her spare bedroom to a lodger to help pay her bills. The lodger gets an affordable place to stay, and the homeowner gets rental income while still living in their own home.

The arrangement differs from having a roommate because the lodger is renting from the homeowner rather than sharing the home equally. A lodger usually has less privacy and independence than someone renting their own apartment, but it costs less and can feel more like living with a family.

You might also hear the word boarder, which is similar but usually refers to someone who also receives meals as part of the arrangement. In the past, taking in lodgers and boarders was much more common than it is today, though some homeowners still rent rooms to lodgers to help cover their mortgage payments or to provide company in an otherwise empty home.