On the mainly island, the majority of the population was and is Greek.
In the early 1970's, the (Greek) habitants of the island were seeking 'enosis', unifining with Greece.
This idea was supported by the greek gouvernment at that time, but against the will of the Turkish minority in the northern part of the island.
In 1974 the Turks occupied the northern part of the country and in 1983 the Turkish Republic of North Cyprus declared itself independent.
Only Turkey recognised the new state, and although Bangladesh and Pakistan initially did the same, they redraw their support after pressiure from the United States.
As for now, the Turkish Republic of North Cyprus is thus only recognised by Turkey, and not by any other country. In this view, the stamps aren 't recognised either, and can be called 'locals', or 'labels for political use'.
However, this summer, a friend of mine went to Cyprus and visited both sides of the island.
He even sent me a postcard from the Northern part (I guess it was sent over Turkey) and the postcard reached my place, cancelled without any problems.
So this means the stamps are valid for postal use.
Some stamps :
|Postcard from TRNC|
|Cancel Turkish Northern Cyprus|