In Britain it is to a large extent governed by social class.
If you are really posh you might call it the drawing room. That has nothing to do with pencil and easel, but it is the room to which one withdraws e.g after dinner.
Lounge is widely used in Britain but perhaps its popularity is relatively recent i.e. since WW2.
Sitting room is still widely used mostly by the polite classes.
The working class term is living room, which is where people do everything - eat, relax, and watch TV. As houses have become larger and people wealthier many have a dining room and a lounge. In houses where they are combined as one - estate agents are apt to call it a lounge-diner.
The parlour which someone said was popular in the American south is very dated in Britain - and was used in houses like Downton Abbey - peopled by the gentry classes.
From the Victorian to the immediate post-WW2 period, lower-middle class homes in Britain often still had what was known as a front-room. This was the best-kept room in the house, the one at the front facing the street. It was used by the family for receiving important guests e.g the vicar, the doctor etc. and on high-days and holidays - such as at Christmas. Families would still continue the Victorian practice of putting an atractive plant by the front window - such as an aspidistra.
This practice was believed by George Orwell to have been emblematic of the determination of that class of British people to present a respectable face to the world - and is central to his 1936 novel Keep the Aspidistra Flying.
In more recent decades Britain's transformation from manufacturing to service economy has changed the social class system, and millions of the industrial terraces which would have sported aspidistras in their "front-rooms" have been demolished. However in parts of inner London, the small terraced houses themselves are alive and well, and have become bijou residences which change hands often for in excess of a million pounds. But families use the houses ergonomically - and the aspidistra is dead.