In the Bible, an upper room was a roof chamber built above the main house, usually for the purpose of leisure. The upper room is most known as the setting of the Last Supper.
In the Old Testament, upper rooms were usually in the homes of kings and the rich. Some verses, such as 1 Kings 17:19, point to upper rooms sometimes serving the purpose of a guest room. Similarly, Mark 14:13-15 states that a disciple offered his upper room's service to Jesus Christ and his apostles. The intimacy that Jesus and the apostles shared during the Last Supper might indicate that an upper room also served the purpose of experiencing privacy.
By the time of the New Testament's writing, upper rooms were more common in Jewish houses. In addition to the upper room used by Jesus, the roof chamber appears in the story of Pentecost following Christ's death, in the story of Tabitha and in the story of Eutychus. Tabitha's corpse was mourned in a roof chamber; this is another example of the room's use for private matters.
According to Acts 1:15, the Pentecost roof chamber held 120 disciples. In contrast with the Last Supper, this number shows that the size of upper rooms could vary widely depending on the house. Similarly, Acts 20 says that Eutychus had to sit in the window of the upper chamber because of its crowdedness. Notably, the Bible states that Eutychus fell from the third story, which shows that upper rooms did not appear solely atop single-floor homes.