A flat is a self-contained housing unit that is part of a larger building with several units. The term "flat" is commonly used in British English, while "apartment" is more commonly used in American English. However, the terms are often used interchangeably. Some people refer to single-storied units as flats because of their "flat" nature. Flats generally have all the basic amenities required for comfortable living, while apartments come with luxury living as well as numerous amenities. Flats are generally occupied by low and middle-class people, whereas the upper and higher class occupies an apartment.

In summary, a flat is a type of housing unit that is part of a larger building, and the term is used more commonly in British English. While the terms "flat" and "apartment" are often used interchangeably, there are some subtle differences in meaning, and the usage is largely dependent on the region.