In short
The potential tax identification number is issued to foreign individuals who have no existing tax liability in Turkey. It is required for title transactions, opening a bank account and setting up utility subscriptions.
The number can be obtained online through the Revenue Administration's digital application system, or in person at a tax office. Passport details are enough for the application, and the number is usually generated the same day.
The word "potential" in the name should not mislead: this is not a temporary record but a permanent number identifying the person within Turkey's tax system. When a tax liability arises in Turkey, the same number carries forward.
Why it matters to an investor
This number is the first link in a foreign buyer's chain of transactions in Turkey. Without it no bank account can be opened; without a bank account no foreign currency exchange certificate can be issued; without that certificate no title transfer can take place. The process has to be built from the beginning, not from the end.