A flatlet is a very small flat — a little apartment of its own, usually with a tiny kitchen and a bathroom, not just a bedroom in a shared house. It is a British word, and it sounds a little old now; younger people more often say studio or small flat. Landlords and older ads still use it. It is not American English. Though actually the first half is British flat (apartment), not a tyre that has gone flat, and the ending only means “a small one of these.” So a flatlet is smaller than a flat, the way a booklet is smaller than a book.

小套房（英式；台灣口語就是套房、小公寓。比雅房完整，多半有自己的衛浴廚房）。