A 'cubiculum' (plural cubicula) was a private room in a 'domus', an ancient Roman house occupied by a high-status family. It usually led directly from the 'atrium', but in later periods it was sometimes adjacent to the 'peristyle'.

It was used for the functions of a modern bedroom, sleep and sex, as well as for business meetings, the reception of important guests and the display of the most highly prized works of art in the house.

The 'cubiculum' was used for quiet or secret meetings and could have been used as a library. It was also a preferred venue for murder and suicide. A room used only for sleeping was not classed as a 'cubiculum'.

More Info: en.wikipedia.org