Grand Maester is a title in Game of Thrones. The Grand Maester is the personal maester to the Iron Throne and the Red Keep. He is a learned man wise in history, science and medicine who also provides counsel. The Grand Maester sits on the King's Small Council, which oversees the day-to-day operations of the realm in the name of the King. The title is currently held by Pycelle.
In the books
While a Grand Maester can conceivably be removed from the Small Council, either by the king or his Hand, the king cannot strip him of his title as Grand Maester. The order of maesters and position of Grand Maester predate the creation of the Small Council by thousands of years, as the council was only formed after the Targaryen Conquest three centuries ago. Kings may still try to influence who gets elected as Grand Maester, similar to how strong kings are sometimes able to influence who gets elected as the High Septon of the Faith of the Seven, but even so this is difficult to achieve. Thus while Tyrion Lannister dismissed Pycelle from the Small Council, it wasn't within his power to strip Pycelle of his rank as Grand Maester.