Daes Dae'mar is a phrase in the Old Tongue which translates to The Great Game, but is more commonly known as The Game Of Houses.
It refers to the political and social maneuvering employed by the nobility of various nations to gain status or wealth, or to cause the downfall of others they dislike.
The Great Game is played the most heavily in Cairhien, where the most seemingly irrelevant act can cause lords and ladies to speculate endlessly about one's motives; even servants of the Cairhienin nobility play their own version of Daes Dae'mar. Conversely, it is rarely seen in the Borderlands, as Borderlanders are more concerned with Shadowspawn and the Blight than individual power, status or wealth.
It has been stated that the best way to put players of the Great Game off balance, is to be honest, since no-one expects you to be. This has been the case with both Rand and Perrin.
Perhaps one of the most accomplished players of the Great Game in current times is Thom Merrilin, who developed his skill at court in Caemlyn. He has used his skill more than once to come to the aid of Rand al'Thor; first in Cairhien while Rand was hunting the Horn of Valere, and later in Tear after Rand proclaimed himself the Dragon Reborn to keep the Tairen High Lords off-balance enough to leave him alone. Another accomplished player of the Game is Moiraine Damodred, whose skillful mind for the Game more than once was annoyed with Siuan Sanche's lack of understanding for it. 
Rand and Perrin have often expressed their dislike of Daes Dae'mar, though Rand has become skilled in it recently.