HMO simply means ‘Houses in Multiple Occupation’ and refers to any property rented to three or more people who are not related to each other. Unless you share with just one other person, or live in a purpose built block, it is likely you will rent an HMO from a private landlord.
HMOs are treated differently in the housing world as they are seen are more vulnerable because the occupants are not a family and therefore do not act like a family. Rules around security, fire safety and waste management differ when the property is an HMO. Some HMOs must have a licence and there are more rules for these larger properties.