terminology (Istanbul)

I am researching online for a rental home in Istanbul. Could someone tell me what a "residence" is? It seems like they are flats to me, but residence and flat are two different choices. Also, many villas seem to be flats, too. Is this true? I would like to know as much as I can before I travel to Istanbul for a house hunting trip in May.

Also, what is the difference between Levent and 4.Levent? I can't find the answer on google.

Many thanks!

Joanne