A waiting room — a place where people wait for their turn or for someone (commonly found in hospitals, stations, government offices, etc.).
病院の待合室で順番が来るのを待った。
I waited in the hospital waiting room for my turn.
電車が遅れていたので待合室は混んでいた。
Because the train was delayed, the waiting room was crowded.
待合室では携帯電話の通話を控えてください。
Please refrain from making phone calls in the waiting room.