Khaleesi of the Great Grass Sea

"You stand in the presence of Daenerys Stormborn of House Targaryen, rightful heir to the Iron Throne, rightful Queen of the Andals and the First Men, Protector of the Seven Kingdoms, the Mother of Dragons, the Khaleesi of the Great Grass Sea, the Unburnt, the Breaker of Chains."

- Missandei introducing Daenerys Targaryen to Jon Snow

Khaleesi of the Great Grass Sea is a title claimed by Daenerys Targaryen. The Great Grass Sea is the region in Essos where the Dothraki roam, and khaleesi is the title given to the wife of a khal in Dothraki culture.

Season 1
Daenerys became a khaleesi upon her marriage to Drogo as arranged by Viserys Targaryen and Illyrio Mopatis, a powerful khal who commanded a khalasar at least 40,000 strong. Drogo eventually impregnated Daenerys, and it was believed by the dosh khaleen that her son, Rhaego, would be the Stallion Who Mounts the World. After Drogo's death, Daenerys, whose son is stillborn, assumes control of the remnants of his khalasar that remain loyal to her.

Season 6
Daenerys is brought before Khal Moro, who states that she must return to Vaes Dothrak to live among with khaleesi widows of the dosh khaleen. At the meeting of the khalar vezhven, however, Daenerys burns the gathered khals and unites their khalasars behind her. For the first time in the history of the Dothraki, they cross the Narrow Sea, following Daenerys.

Season 7
When Jon Snow is brought before Daenerys at Dragonstone, Missandei formally introduces her with her many aliases and titles, Khaleesi of the Great Grass Sea among them. The khaleesi Daenerys, mounted atop Drogon, later uses her united Dothraki khalasar to attack the Lannister-Tarly army at the Battle of the Goldroad.

In the books
In the A Song of Ice and Fire novels by George R.R. Martin, similar to the TV show, Khaleesi of the Great Grass Sea is one of the many titles claimed by Daenerys Targaryen.