bedroom; sleeping quarters
Often implies a married couple's bedroom; somewhat literary or old-fashioned. In modern casual speech, 寝室 (しんしつ) is more common.
The couple returned to their bedroom.
inner room; back room
Refers to a room located deep inside a house, away from the entrance. This usage is rare and mostly found in descriptions of traditional architecture.
In old Japanese houses, the sleeping quarters were located in the back.
寝屋 can also refer to the innermost room of a house.
sexual intercourse; lovemaking
Standard kanji spelling; 寝 (sleep) + 屋 (room/shop) clearly conveys 'sleeping room'.
Literary or archaic kanji for bedroom, especially a married couple's room. Rare in modern writing.
Compound of 寝 (ne, 'sleep') + 屋 (ya, 'room/house'). The kanji 閨 is a specific character for a bedroom, often a married couple's room, and is used as an alternative spelling.