Khalasar

A khalasar is a Dothraki clan or tribe. Khalasars can be quite small but can expand to encompass tens of thousands of riders and many more than that in women and children. Khalasars are spread across the Dothraki sea and frequently raid surrounding regions. Khalasars which meet on the plains usually engage in battle, except at Vaes Dothrak where no weaponry is permitted due to the illegality of bloodshed within the city. However, that does not mean that violence is unheard of, with Dothraki devising cunning means to kill without the use of steel or shed blood.

In the books
In the Song of Ice and Fire novels, a khalasar is a tribe of horse riders that can count tens of thousands of Dothraki riders. They are led by a khal. Dothraki are born and die in the saddle. A Dothraki warrior will braid his hair with bells, only cutting his hair if he is defeated in battle.