Pashtunistan (Pakhtunistan) is a "Land of Pashtuns" which was politically divided in 1893
by the Durani Line, a disputed and poorly-marked border between Afghanistan and British India.
Since the late 1940s with the dissolution of British India and creation of Pakistan, Pashtun nationalists
proposed returning the land to Afghanistan or creating a Pashtunistan as a future sovereign state
for the local Pashtun inhabitants of the area.
Needless to say it remains a point of contention between Afghanistan and Pakistan and foced
the latest to rename the Northwest Frontier Province to Khyber Pakhtunkhwa and to give local Pashtuns
more sary in governing themselves.
Total number of Pashtuns is about 50 million in both countries.Note that this flag has another version which you can find in this [link]