A rule passed by a city or town council. For example, most cities or towns in Ontario have "property standards" by-laws, which say that buildings must be kept in good repair. Tenants have the right to have their landlords comply with these standards. Some by-laws might say how many people are allowed to live in one apartment, depending on its size.
Corporations (companies) also have by-laws. For example, a housing co-operative or a condominium corporation might have by-laws that affect the rights of tenants, members, or owners.