A lodger is someone who pays rent for a room in another person’s house. They do not usually take the whole house or a separate flat; they share the front door with the owner, and often the kitchen or bathroom. The owner is the landlord or landlady; the lodger pays for that room. It is a British-flavoured word. American English more often says roommate or boarder, though a boarder often gets meals too. Though actually lodging is the room, and board is the food — that is why the two sit so close. The person-ending -er simply means “one who lodges.”