Parley

A parley is a conference or discussion, particularly in military affairs. During a conflict or dispute, representatives of the involved parties will meet in good faith to negotiate a peaceful resolution to the issue. An envoy may approach the other party carrying a peace banner, such as a white flag, to indicate their wish to parley. Much like with guest right, it is considered heinous to harm a foe during a parley.

Notable parleys

 * Stannis Baratheon and his younger brother Renly, both claimants to the Iron Throne, meet to discuss a peace. They trade insults and it is quickly apparent that neither will submit to the other. Catelyn Stark's exhortations for them to reach an agreement make no difference and the brothers part, each vowing to destroy the other.
 * Daenerys Targaryen meets with Razdal mo Eraz, one of the Wise Masters of Yunkai in her tent outside the city. He pleads with her not to attack the city, and first threatens her, then attempts to bribe her with ships and chests of gold. Daenerys counters with her own offer: she will show mercy, if all the slaves of the city are freed. When her dragons snap at Razdal, he nervously reminds her that she guaranteed him safe conduct, but she retorts that her dragons did not. He leaves, threatening retribution from Yunkai's powerful friends.
 * On Ramsay Snow's orders, Theon Greyjoy treats with the ironborn garrison which holds Moat Cailin. He approaches the castle on horseback, carrying a white flag. Theon convinces the ironborn to surrender (after they murder their commander Ralf Kenning) and are promptly massacred by Ramsay.
 * Following the Battle of Castle Black, Jon Snow leaves to seek out Mance Rayder on the pretext of parleying with him, though Jon actually intends to assassinate the King-Beyond-the-Wall. They meet in Mance's tent and share a toast to the fallen from both sides. Mance realizes Jon's real intention when he notices him eyeing a knife. He chides him for considering killing a man who offered to parley and discuss peace in good faith. They are interrupted by Stannis Baratheon's approaching army.

In the books
After Renly's death, most of his bannermen defect to Stannis, but Storm's End continues to hold out under Ser Cortnay Penrose. Ser Cortnay parleys with Stannis outside the castle walls, but refuses to yield. When he insults Stannis and the Lord of Light, Ser Guyard Morrigen snaps: “Be glad this is a parley, Penrose, or I would have your tongue for those words.”

An army led by Ser Rodrik Cassel besieges Winterfell after it is captured by Theon Greyjoy. Cley Cerwyn appraoches the gates with a peace banner, indicating that the besiegers seek a parley. Theon leaves the castle walls to negotiate with Ser Rodrik. Theon is hopelessly outnumbered, and knows that he cannot hold Winterfell for long without assistance, but remains defiant. He reveals his trump card: Ser Rodrik's daughter, whom he threatens to hang if the besiegers attack. He hurriedly returns to the castle, fearing he may be picked off by an archer, despite the oath.