What did the Imams mean by "Masjid al-Bayt" (Mosque of the House), what is the difference between it and a regular mosque, are there criteria for applying this description to a place, and what are the rulings associated with it?

The scholars agree that i'tikaf (spiritual retreat) is only valid in mosques and is not permissible in homes. As for the prayer areas within homes (masajid al-buyut), they are merely places for prayer and do not take on the rulings of endowed mosques. Therefore, i'tikaf is not valid in them. It is permissible for a menstruating woman and someone in a state of major ritual impurity (junub) to stay in them, and praying in them does not carry the same virtue as praying in mosques. What has been narrated from some of the Salaf regarding i'tikaf in home prayer areas contradicts the apparent meaning of the texts and the consensus of the majority of scholars.