Khalar Vezhven

Daenerys Targaryen is brought before the Khalar Vezhven.

"Ei khalasari ray essash vaesaan ershe haji Khalaroon Vezhvena, fini ashiloe mori ajerie ostirge mori haji aheshkoon sila meshes. Mori avokkeri ma fin vaes nem vemrasoe, ma fin yanqosori nem vazzafroe, ma fini nem vohhari. Ma ajjin mori’th vokkeri fasqoy khaleeni ma norethoon vizhada Khali Drogo."
"All the khalasars have returned to the ancient city for the Khalar Vezhven, where they will meet to discuss their plans for the coming winter. They will decide which cities will be sacked, which tribes will be enslaved, and which ones destroyed. And now they must decide what to do with Khal Drogo’s silver-haired widow."

―The High Priestess to Daenerys Targaryen

The Khalar Vezhven is a great gathering of all the Dothraki khalasari at their capital (and only) city, Vaes Dothrak in the Dothraki Sea.

The assembled khali discuss and decide which lands to raid and which tribes to enslave. It is unclear how frequently each gathering occurs.

According to the High Priestess, a Khalar Vezhven is imminent, and one of the things the khali will decide is the fate of Daenerys Targaryen, who violated Dothraki tradition by venturing out into the world instead of joining the dosh khaleen immediately after the death of her khal. During this gathering, the khali deemed Daenerys unworthy of becoming a dosh khaleen and in response, she killed every khal in attendance as well as numerous bloodriders by knocking over every flaming brazier in the building, setting it ablaze. When she emerged unscathed, every surviving Dothraki outside swore their allegiance to her, restoring her title as khaleesi, albeit with a much larger force of 100,000 at her command.

In the books

In the A Song of Ice and Fire novels, the specific Khalar Vezhven seen in the TV series has not yet occurred, because Daenerys is only captured by the Dothraki in the last chapter of the most recent novel (corresponding to the Season 5 finale).

The overall custom of an assembly called a Khalar Vezhven has actually not been described in the novels - yet.

The prior novels did vaguely mention that Vaes Dothrak is large enough to hold all of the Dothraki khalasars when they periodically all return to the city, apparently for different cultural gatherings or religious ceremonies, etc.

"Vezhven" means "Great", "Khalar" might mean "gathering of Khals".

The concept of the Khalar Vezhven is similar to the real-world kurultai, where the Mongol khans gathered to discuss important issues, including future invasions and the election of a new Great Khan.