Not every culture has two-stories suburban homes the same way that America (and many other Western countries do). However, there it is common to have a set up where there's an area where guests are received and a more private area where the resisidents sleep and guests more rarely go. You see this set up commonly in American apartments: living room in the front, bedrooms at the back.

In Turkey and parts of the Muslim these two areas were codified with names. There was the public facing selamlık and private haremlik. Selam is a phrase that means greeting (hi, hello, though etymologically ultimately it implies peace or wholeness), so that is the area where one greats their guests. Haremlik you notice has the same root (H-R-M) as haram, which mean forbidden, not acceptable, in Islam. However, you notice that the same root is used in other words, notably harem (where the wives of the sultan or other important person lived) or Al-Masjid al-Haram (the Great Mosque in Mecca, sometimes translated as the Holy Mosque where Haram means holy) or Al-Haram Al-Sharif (the Noble Sanctuary, i.e. the Temple Mount in Jerusalem, where Sharif means noble and Haram is being used as a noun and translated as Sanctuary). What H-R-M means is not forbidden but really "set apart", whether for a holy purpose as in the holy sites mentioned, or because it is ritually unclear, or set apart as a private space/a space for women.

This differentiation into semi-public and truly private isn't universal (many cultures have traditionally had completely different living arrangements, whether group long house or one room buildings) but it certainly is common, especially for prestigious people who could afford multiple rooms or multiple stories. I know in Turkey, as more people became wealthy, this orientation became more common (the anthropologist Michael Meeker writes a little bit about it) and possibly an explicit display of status. In many villages as recently as the 1950's, sometimes only one or two people had a "guest room" (sometimes just called a "room") in which to receive guests. These days, everyone has multiple rooms and it's very common to see the same basic design concept up a semi-public public space to receive guests and a truly private space for women/sleep remains. Likely, a similar thing happened in the West, and this former sign of status became simply the natural arrangement.