As the name indicates, a flat is a dwelling where everything is on one level. That is what differentiates it from an apartment. The term is typically one used in the UK but it is also frequently used in other locations too. It is common for a flat to be part of commercial property that is rented out for income. It may be referred to as a unit in many locations, including the USA.
There are usually many blocks of flats that are all owned by the same individual or the same business. They are rented out for a monthly fee and there is usually some terms such as a 1 year lease.
Each flat is a self-contained unit and the renter will have access to a kitchen, bathroom, bedroom, and living room. There is usually just the basics with this type of living arrangement. It works well for single adults, for college students, and for those that really need to cut out additional expenses for one reason or another.
A flat is a great idea for someone who has mobility issues. They aren’t able to get around well with stairs. Since a flat provides them with everything they need on one level, it can reduce the risk of the elderly falling. It can also help with keeping young children off of stairs.