A private habitation in a home or building that is divided into multiple distinct abodes is called an apartment.

There may be one or more small rooms in an apartment.
A flat is an apartment; it often consists of a number of rooms that you rent in a building.

Your flat could be above your parents’ garage or in a posh high rise with a doorman and an elevator.
An apartment has been defined as “separate rooms within a house” since the 1640s. The word “apartment” is an Italian word that literally translates to “a divided area.”
Every apartment is a unique room or group of rooms where individuals can dwell. Tenants may occasionally have to share a tiny room in an apartment as well as the kitchen and bathroom.

a room or group of rooms designed specifically for habitation.
Only one entrance hallway leading to several units will be shared by tenants.
A residential unit with its own door, bathroom, and kitchen is referred to as an apartment.