The Long Exile is the name given to the period when the Ogier lost track of the stedding and began to succumb to the sickness of the Longing. This period spans much of the Breaking of the World and some of the succeeding generations before the Ogier found the stedding again.
Despite the 3,500 years that have passed since the Exile, the Ogier still suffer from the Longing if they spend more than a few years outside the stedding without returning. The Ogier of Seanchan did not suffer from the Exile, as they never lost track of the stedding, which were more numerous on their landmass.