A roommate is a person who shares a living facility such as an apartment or dormitory. Similar terms include suitemate, housemate, flatmate ("flat": the usual term in British English for anapartment), or sharemate (shared living spaces are often called sharehomes in Australia,^{[citation needed]}). In the UK, the term "roommate" means a person living in the same bedroom, whereas in the United States, "roommate" and "housemate" are used interchangeably regardless whether a bedroom is shared. This article uses the term "roommate" in the US sense of a person one shares aresidence with who is not a relative or significant other. The informal term for roommate is roomie,^[1] which is commonly used by university students.

The most common reason for sharing housing is to reduce the cost of housing. In many rental markets, the monthly rent for a two- or three-bedroom apartment is proportionately less per bedroom than the rent for a one-bedroom apartment (in other words, a three-bedroom flat costs more than a one-bedroom, but not three times as much). By pooling their monthly housing money, a group of people can achieve a lower housing expense at the cost of less privacy. Other motivations are to gain better amenities than those available in single-person housing, to share the work of maintaining a household, and to have the companionship of other people.

Roommates are a fairly common point of reference in Western culture, especially in North America. In the United States, most young adults spend at least a short part of their lives living with roommates after they leave their family's home. Therefore, many novels, movies, plays, and television programs employ roommates as a basic principle or a plot device. On the other hand, it is less common for people of any age to live with roommates in some countries, such as Japan, where single-person one-room apartments are plentiful.

There are many different forms of flat shares also, from the more established flat shares where the flatmate will get their own room that is furnished to "couch surfing" where people lend their sofa for a short period.

Many universities in the United States require first-year students to live in on-campus residence halls, sharing a dormitory room with a same-sex roommate.

One difficulty is finding suitable roommates. Living with a roommate can mean much less privacy than having a residence of one's own, and for some people this can cause a lot of stress.

Another thing to consider when choosing a roommate is how to divide the cost of living. Who pays for what, or are the shared expenses divided between the two or more roommates. Also, the potential roommate should be trusted to pay their share and trusted to pay it on time. Sleeping patterns can also be disrupted when living with a number of people, so it is therefore important to choose housemates wisely.

sources from : http://en.wikipedia.org/wiki/Roommate