From A Wiki of Ice and Fire
The dosh khaleen are a group of Dothraki crones that live in Vaes Dothrak. They are collectively former khaleesis, the wives of khals that have died. They are the only permanent residents of Vaes Dothrak. They enjoy great honor and status amongst the Dothraki and serve as seers foretelling the future and interpreting omens for the Dothraki. They are served by eunuchs.
The prospective wives of khals must be presented to the dosh khaleen for acceptance.
In A Game of Thrones the crones declare that the son of Daenerys Targaryen and Khal Drogo will be The Stallion Who Mounts the World, a great conqueror whose coming is long foretold in Dothraki prophecies.