Studio	A one-room apartment with separate bath and sometimes a separate kitchen. These can range from very small (big enough for a sofa bed and a desk) to very large (can accommodate a king-size bed and have a separate sitting area and dining area). An alcove studio has an alcove, or distinct separate area or nook for dining or sleeping. Generally, alcove studio implies a larger apartment than a straight-line studio. Often they are configured in a L shape, or they may have an area separated by an archway that can be sectioned off as a separate room. A convertible studio is a studio large enough to section off a separate sleeping area or bedroom. It can be either a straight-line studio or an alcove studio.
One bedroom	An apartment with a separate bedroom and a living area. Some have full separate kitchens, some do not. A junior one-bedroom usually implies an extra-large studio or small loft, large enough to section off a separate sleeping area or bedroom. A "three-room" may be an apartment with a third room that is not conveniently situated to be practical as a separate bedroom or full living room, such as in a railroad layout. These apartments are most often found in older walkup buildings that have smaller rooms. A junior 4 is a large one-bedroom that usually has a full separate kitchen and a separate dining area, large foyer, or living room big enough to section off. Most junior 4 apartments can be converted into a two-bedroom.
Two-Bedrooms	A full 2-Bedroom or "real 2-Bedroom" has two actual, separate bedrooms plus a living room, and may or may not have a separate kitchen.  A convertible 2-Bedroom, or "flex 2" is a one-bedroom large enough and laid out in such a way that a wall could be put up to create a second bedroom. A wing apartment has two bedrooms and a small common area such as an eat-in kitchen, but no real living room. These apartments are commonly found in Greenwich Village and are good for students or roommates who don't require much in the way of common living space.
Three-Bedroom	As its name implies, this apartment offers three separate bedrooms. Common space, kitchen, and size of the bedrooms can vary widely. A convertible 3-bedroom is a 2-bedroom large enough and laid out in such a way that it can be converted into 3 bedrooms. A "classic 6" is a 3-bedroom apartment - usually found in turn-of-the-century luxury buildings - that was originally designed with two bedrooms, a maid's room, full dining room, living room, and kitchen. It is important to note that the sizes of bedrooms within a three-bedroom apartment can vary greatly.
Loft	This is a big, open space that usually results from a conversion of commercial building into residential units. Lofts generally have very high ceilings and extra-large windows. Some are open spaces with few internal walls; others have been constructed into one, two, or more bedrooms. They are mostly found in commercial neighborhoods.
Duplex	This is an apartment with two levels. It can be a legitimate bi-level apartment with an enclosed upstairs and downstairs areas, or it can be an open space with an extra-high ceiling and a loft or mezzanine.
Triplex	Same as duplex, but with three levels.
Railroad Apartment	One room leads into another and there are no separate hallways.
Share	One room for rent in a two or more bedroom apartment already occupied by one or more tenant.
Building Terminology
Brownstone	One to six floors. No doorman. Built in the early 1900s as single family homes and many were converted during World War II to create multiple apartments (3-10 units per building.) Brownstones have "charm." Square footage is generally less than what similar room count would provide in a doorman building. Very few brownstones have elevators.
Elevator building	Four to twenty stories. Many are found on side streets and are nine stories tall and have a laundry. Some pre-wars have an elevator attendant.
Loft apartment	Four to eleven or twelve story buildings. Former commercial buildings converted to apartments. Large open space. Usually elevator but no doorman service. Most are found in lower Manhattan in SoHo. Tribeca or Chelsea.
Luxury (doorman)	Five to forty or more floors. Full or part-time doorman. The more luxurious buildings also have a concierge that provides services such as receiving laundry and packages. Some of these buildings have a health club and/or swimming pool.
Prewar building	Ten to thirty floors. Doorman or non-doorman. Built in the late 1800s to 1940s. Exterior and interior architectural detailing. Common features include high-ceilings, hardwood floors, arched doorways or fireplaces. Most are co-ops.
Postwar building	Built after 1946. Exteriors are usually white, red or brown brick. Most are cheaper than prewar. Laundry facilities are usually in the basement.
Walk-up building	Up to six story building constructed in the early 20th century. It does not have an elevator, and most likely it does not have an on-site laundry facility. There is no doorman, and security is generally a locked double-door with an intercom to welcome guests. Most walkups have been renovated, and many are still rent-stabilized, offering the best value for the money.
Other Common Terms
Live/work	Usually refers to a commercial building where some residential tenancy is accepted. A live/work space has a kitchen and full bathroom with shower.
Commercial Loft	Zoned for business use only. This loft usually has no kitchen and a small bathroom with no shower.
Sleep Loft	This is an add-on structure usually found in apartments with high ceilings (10 to 14 feet or more). Typically it's like the upper part of a bunk bed, with a ladder leading up to it. It usually accommodates at least a double-size mattress, although some are larger. The space below is often used as a closet or desk space, and the higher the ceiling, the more comfortable a sleep loft will be to sleep in.
Furnished Apartments	Can include basic furniture and dishes, utensils, small appliances, etc. Generally about 20% more expensive than their unfurnished equivalent.
Balcony or Terrace	Often used interchangeably to indicate an outdoor railed platform extending from the apartment. It usually has a roof provided from the balcony/terrace of the apartment above.
Roof Terrace or Roof Deck	This implies a larger terrace or patio provided by the roof of the extended floor below. It usually has brick wall barriers around the perimeter, is open to the sun, and some wrap around the corners of the building.
Garden or Backyard	Many ground floor apartments offer private access to the backyard. It can be tiny or large, and in larger buildings with multiple rear exits, it may be semiprivate or shared.