An apartment is a type of housing unit that occupies someplace in a building, usually a floor. The apartment or flat refers to the housing units with one, two, or three bedrooms with attached bathrooms, a balcony, a drawing room, and a Kitchen. There is a slight difference between a flat and an apartment; flats are built on an old building after reconstruction, whereas apartments are purposely built units. Apartments are usually constructed on apartment buildings (a multi-story building with more than three apartments is known as an apartment building). There are different types of apartments, such as studio apartments, salon apartments, Maisonette, penthouse, serviced apartments, etc. Apartments for rent are available; the owners may rent out his/her apartment fully furnished, partially furnished, or without any furniture. Most apartments have a shared laundry, an electrician, a plumber, a security system, and a parking lot. The history of apartments/flats can be traced back to the times of the Roman empire. The Roman used to build such infrastructures that can be categorized as apartments. The modern history of apartments goes back to the 17th century when Yemenis started building 7 to 11 story buildings. According to the census of 2011, 52% of the houses in London are apartments.