Multi-family residential (also known as Multi-dwelling unit or MDU) is a classification of housing

House

A house is a building or structure that has the ability to be occupied for dwelling by human beings or other creatures. The term house includes many kinds of different dwellings ranging from rudimentary huts of nomadic tribes to free standing individual structures...

 where multiple separate housing units for residential (i.e. non-commercial) inhabitants are contained within one building or several buildings within one complex. A common form is an apartment building. Sometimes units in a multi-family residential building are condominium

Condominium

A condominium, or condo, is the form of housing tenure and other real property where a specified part of a piece of real estate is individually owned while use of and access to common facilities in the piece such as hallways, heating system, elevators, exterior areas is executed under legal rights...

s, where typically the units are owned individually rather than leased from a single apartment building owner.

Many intentional communities

Intentional community

An intentional community is a planned residential community designed to have a much higher degree of teamwork than other communities. The members of an intentional community typically hold a common social, political, religious, or spiritual vision and often follow an alternative lifestyle. They...

 incorporate multi-family residences, such as in cohousing

Cohousing

A cohousing community is a type of intentional community composed of private homes supplemented by shared facilities. The community is planned, owned and managed by the residents – who also share activities which may include cooking, dining, child care, gardening, and governance of the...

 projects.

Types

• Two-flat - a building
  Building
  In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...
  
   basically like a house
  House
  A house is a building or structure that has the ability to be occupied for dwelling by human beings or other creatures. The term house includes many kinds of different dwellings ranging from rudimentary huts of nomadic tribes to free standing individual structures...
  
  , commonly built on a house lot
  Lot (real estate)
  In real estate, a lot or plot is a tract or parcel of land owned or meant to be owned by some owner. A lot is essentially considered a parcel of real property in some countries or immovable property in other countries...
  
  , consisting of a flat (apartment
  Apartment
  An apartment or flat is a self-contained housing unit that occupies only part of a building...
  
  ) taking up the first floor, another flat taking up the second floor, usually a common basement
  Basement
  __FORCETOC__A basement is one or more floors of a building that are either completely or partially below the ground floor. Basements are typically used as a utility space for a building where such items as the furnace, water heater, breaker panel or fuse box, car park, and air-conditioning system...
  
  , a common front entrance, foyer
  Foyer
  A foyer or lobby is a large, vast room or complex of rooms adjacent to the auditorium...
  
  , and stairs
  Stairs
  -People:* Scott Kannberg , guitarist of Pavement* A. Edison Stairs , New Brunswick politician* Denis Stairs , engineer, Montreal businessman* Ernest W. Stairs , New Brunswick politician...
  
   to the second floor, and often a similar back entrance, foyer, and stairs. In old buildings, the back entrance, foyer, and stairs may have been added on later. Sometimes there are front verandas for each of flats, one above the other. Typically the whole building is owned by the same party. '
• Three-flat - a building similar to a two-flat except there are three flats. Two-flat and possibly three-flat buildings are rather common in certain older neighborhoods in certain cities.
• Four-flat - a building similar to a three-flat except there are four flats. In some cases, the arrangement of apartments may be different and the lot size may be larger than that of a regular house.
• Duplex
  Duplex (building)
  The term duplex can be used to describe several different dwelling unit configurations:A duplex house is defined as a dwelling having apartments with separate entrances for two families. This includes two-story houses having a complete apartment on each floor and also side-by-side apartments on a...
  
   or semi-detached
  Semi-detached
  Semi-detached housing consists of pairs of houses built side by side as units sharing a party wall and usually in such a way that each house's layout is a mirror image of its twin...
  
  - One building consisting of two separate "houses", typically side by side, each with separate entrances and typically without common inside areas. Each of the two houses typically has separate owners.
• Townhouse
  Townhouse
  A townhouse is the term historically used in the United Kingdom, Ireland and in many other countries to describe a residence of a peer or member of the aristocracy in the capital or major city. Most such figures owned one or more country houses in which they lived for much of the year...
  
   - a house
  House
  A house is a building or structure that has the ability to be occupied for dwelling by human beings or other creatures. The term house includes many kinds of different dwellings ranging from rudimentary huts of nomadic tribes to free standing individual structures...
  
   attached to any number of other townhouses each of which may have multiple floors, commonly side by side each with their own separate entrances. Each such house has its own owner.
• Apartment building - a building
  Building
  In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...
  
   with multiple apartments. There can be multiple apartments on each floor and there are often multiple floors. Apartment building can range in many sizes, some with only a few apartments, other with hundreds of apartments on many floors, or any size in between. There are often inside hallways and inside entrances to each apartment, but outside entrances to each apartment are also possible. An apartment building can be owned by one party and each of the apartments rented
  Renting
  Renting is an agreement where a payment is made for the temporary use of a good, service or property owned by another. A gross lease is when the tenant pays a flat rental amount and the landlord pays for all property charges regularly incurred by the ownership from landowners...
  
   to tenants or each of the apartments can be owned as a condominium
  Condominium
  A condominium, or condo, is the form of housing tenure and other real property where a specified part of a piece of real estate is individually owned while use of and access to common facilities in the piece such as hallways, heating system, elevators, exterior areas is executed under legal rights...
  
  by separate parties.
• Mixed use building - a building with space for both commercial, business, or office use, and space for residential use. Possible arrangements include the commercial/business use on the first or first couple floors and one or more apartments or residential spaces on the upper floors. Another possibility is to have the commercial/business area up front and the residential area in the back. Some or maybe all of the space may be used by the owner or some or all the business and residential units may be leased by the owner. Condominium ownership is also possible.
• Apartment Community - A collection of apartment buildings on adjoining pieces of land, generally owned by one entity. The buildings often share common grounds and amenities, such as pools, parking areas, and a community clubhouse, used as leasing offices for the community.