Kayla

"Kayla is famous here to Volantis... in certain circles. One of the four women in the world who can perform a proper Meereenese Knot."

- Tyrion Lannister

Kayla is a character in the third season. She's portrayed by contortionist Pixie Le Knot.

Biography
Kayla is one of the four women in the known world who can bend her body for a sexual position known as the "Meereenese Knot".

Season 3
Kayla is a prostitute in one of Petyr Baelish's brothels. Along with Marei and Genna, she is one of the three prostitutes hired by Tyrion Lannister to service Podrick Payne as a reward for saving his life in the Battle of the Blackwater.

In the books
In the A Song of Ice and Fire novels, there's no character named Kayla. The "Meereenese Knot" is an inside joke to the books fandom about a major plot issue George R. R. Martin had to deal with when writing A Dance With Dragons.