The Amyrlin Seat is a fictional title from Robert Jordan's Wheel of Time series.
The Amyrlin Seat, or Amyrlin as it is often shortened to, is the leader of the Aes Sedai in Tar Valon. The term can also refer to the actual seat upon which the Amyrlin sits. She is chosen by the Hall of the Tower for life, and forsakes her former Ajah to be seen as "from all Ajahs and yet of none." Hers is the supreme authority among the Aes Sedai, although she can be deposed for malfeasance by the Sitters in the Hall.
It is a position held only by a female who can channel, and presumably only by one who belongs to the White Tower. White Tower law considers the Amyrlin Seat to be an Aes Sedai after having been raised, but does not require it as a prerequisite for raising. This loophole was used to raise Egwene al'Vere to the position by the Salidar Aes Sedai.
In the Age of Legends, Aes Sedai who sat as the "First Among Servants" (such as Lews Therin Telamon) were the equivalent of the modern-day Amyrlin Seat. These Firsts wore the ring of the Tamyrlin. "Amyrlin" is presumably a corruption of this Old Tongue word, though the likely reality is that it is a literary allusion to Merlyn the Magician, just as Tar Valon is an allusion to Avalon.
(*)- Her efforts to control Artur Hawkwing almost split the White Tower, and she was stripped of her stole and punished severely as a result of this. She was the last Aes Sedai of the Red Ajah to be raised as Amyrlin, until Elaida do Avriny a'Roihan was raised to the Seat.