In English, this term refers to a mansion, a citadel, or the older part of a town in North Africa. It came into English by way of Colonial French. The Arabic derivation is somewhat obscure.

The original site of many a Middle Eastern and North African city or town is a walled complex, resembling a forte. Population increase would typically lead to the expansion of the town into a modern, sprawling metropolis, while keeping the old castle intact, until, in some cases, it succumbs to its natural demise. These old fortress (I was born in one) is often called "Al-Qal’a" القلعة (The Castle). This became the name of a Spanish town (you may have heard of the "Alcala barber" if you studied formal logic) as well as a Spanish family name (A Spanish president as well as several famous Spanish athletes have had this name).

In North Africa, the name for such an entity was "qasba" قصْبة. It may be the local pronunciation of the Arabic word "qasaba" قَصَـبة, meaning the main part of a town or the main town in a region ("Kasaba" is the name of a twon in Cyprus as well as a city in Turkey).

But qasba may also have been derived from the verb "qasaba" قَـصَـبَ which refers to the stone cutting involved in the construction of these formidable structures.

Whatever the origin may have been, the French used the term to refer to the old parts of the towns around which they established their colonial presence. The term eventually found its way into English.

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