The Meereenese knot refers to the plotline in Meereen in A Dance with Dragons which George R.R. Martin took some time to sort out, as several of the storylines and characters converge in Meereen. Martin attributed the delay mainly to his untangling "the Meereenese knot", which the interviewer understood as "making the chronology and characters mesh up as various threads converged on Daenerys". According to GRRM,
Now I can explain things. It was a confluence of many, many factors: lets start with the offer from Xaro to give Dany ships, the refusal of which then leads to Qarth's declaration of war. Then there's the marriage of Daenerys to pacify the city. Then there's the arrival of the Yunkish army at the gates of Meereen, there's the order of arrival of various people going her way (Tyrion, Quentyn, Victarion, Aegon, Marwyn, etc.), and then there's Daario, this dangerous sellsword and the question of whether Dany really wants him or not, there's the plague, there's Drogon's return to Meereen... All of these things were balls I had thrown up into the air, and they're all linked and chronologically entwined. The return of Drogon to the city was something I explored as happening at different times. For example, I wrote three different versions of Quentyn's arrival at Meereen: one where he arrived long before Dany's marriage, one where he arrived much later, and one where he arrived just the day before the marriage (which is how it ended up being in the novel). And I had to write all three versions to be able to compare and see how these different arrival points affected the stories of the other characters. Including the story of a character who actually hasn't arrived yet. 
Game of Thrones
Kayla, a prostitute working in the brothel owned by Petyr Baelish in King's Landing, can perform the sexual position called the "Meereenese Knot", a reference to the complex series of plot problems George R.R. Martin encountered whilst writing the fifth novel in the series, A Dance with Dragons, problems which delayed the novel for a considerable amount of time.
- The Problems of Power: George R.R. Martin's A Dance With Dragons. By James Poniewozik, July 12, 2011
- So Spake Martin. Asshai.com Interview in Barcelona July 28, 2012.