Moonsingers

"Then I turn left onto Moonsinger Lane..."

- Arya Stark describes her daily routine in Braavos to Jaqen H'ghar

The Moonsingers priestesses of the Jogos Nhai religion. They are also present in the Free City of Braavos, because some of the escaped slaves from the Valyrian Freehold that founded Braavos were Jogos Nhai.

Season 5
Arya Stark describes her daily routine as an oyster-cart girl named "Lanna" to Jaqen H'ghar. As she describes the route she takes through the city, she mentions "Moonsinger Lane".

In the books
In the A Song of Ice and Fire novels, the Moonsingers are the priestesses of the Jogos Nhai, the culture of mounted raiders that live in the plains north of Yi Ti, and east of the massive Bone Mountains that divide them from the Dothraki to the west.

Although the Jogos Nhai and their Moonsingers have been mentioned in passing since the first novel, little detail was given about them, as their homeland is located far east of even the Dothraki Sea. A little more information was given about them in the fourth novel when Arya Stark arrives in Braavos: Denyo Terys (son of Ternesio Terys, the ship captain that transports Arya to the city from Westeros) explains to her that Braavos was founded by a diverse group of slaves form the Valyrian Freehold that overthrew the overseers in the slave ship fleet they were being transported in, and then fled as far away from Valyria as they could. The slaves were from many different peoples, cultures, and religions (Andals, Rhoynar, Ghiscari, Summer Islanders, even imprisoned Valyrians) but one group that rose to prominence among them were the Moonsinger priestesses of the Jogos Nhai. Based on their visions, the Mooonsingers led the escaping fleet to the extreme northwest corner of Essos, where they found a hidden lagoon which was an ideal place to take refuge in, and where they founded Braavos. The Braavosi still welcome all faiths in their city and has no one majority religion, but the Moonsinger religion is still quite revered and has more followers than any other single religion in the city - explaining why the Temple of the Moonsingers in Braavos is the largest temple in Braavos.

The World of Ice and Fire sourcebook (2014) introduced the first detailed description of the Jogos Nhai and their culture. The Jogos Nhai have very different views about gender compared to people living in Westeros. Each band of the Jogos Nhai is co-ruled by a jhat and a moonsinger. The jhat is a war leader, in charge of external politics. The moonsinger is a combination priestess/healer/judge, in charge of internal domestic affairs. If a woman wants to be a jhat, however, she must dress and live as a man, while if someone born a man wishes to be a moonsinger, he must dress and live as a woman. It is very difficult for outsiders to even tell if a band's moonsinger was born a man or a woman, as they are treated and referred to as women by everyone else in their band.

The main novels do mention that the Moonsingers are a prominent religion in Braavos, but none have been met in the narrative. It is unknown if, like in their homeland in the distant east, some Moonsingers in Braavos are actually men who choose to live as women.