From A Wiki of Ice and Fire
A maidenhead is a euphemism for a girl or woman's virginity, referring to the anatomical hymen. A woman who has lost her virginity can be described as to having been “deflowered”  and will no longer be referred to as a maiden or a maid. For a highborn woman, the absence of a bloody bed sheet on her wedding night means little, as a lord’s daughter does not always have a maidenhead due to horse riding. A common peasant girl is more likely to have retained her maidenhead until consummation. 
A virgin whore’s maidenhead can cost a golden dragon.  (about £11,111.00 in today’s money). At Renly Baratheon's camp some young knights, one of whom was Ser Hyle Hunt, wagered on who would be the first to take Brienne of Tarth’s maidenhead. Each man was required to buy into the contest with a golden dragon, the whole sum was to go to whoever claimed her virginity. 
|“||Drogo’s khalasar was mine. I bought them from him, a hundred thousand screamers. I paid for them with your maidenhead.||”|
|“||"Worms will have your maidenhead. Your death is here tonight, little one. Can you smell her breath? She is very close."||”|
|“||Emma had decreed that Rosey's maidenhead would cost a golden dragon.||”|
|“||"It was only a game to pass the time. We meant no harm." ||”|
|“||I am old now, a dried-up thing, too long a widow, but I still remember the look of my maiden’s blood on his cock the night he claimed me.||”|
|“||"A score or more of Walder Frey’s sons and grandsons began to bang their cups again, shouting, “To bed! To bed! To bed with them!” Roslin had gone white. Catelyn wondered whether it was the prospect of losing her maidenhead that frightened the girl, or the bedding itself. With so many siblings, she was not like to be a stranger to the custom, but it was different when you were the one being bedded.||”|
|“||"Her maidenhead is not intact.” ||”|
|“||"I can only swear to the truth of what I discovered for myself when I examined the queen." ||”|
References and Notes
- ↑ A Storm of Swords, Chapter 19, Tyrion, p 221.
- ↑ 2.0 2.1 A Feast for Crows, Chapter 28, Cersei.
- ↑ 3.0 3.1 A Feast for Crows, Prologue.
- ↑ 4.0 4.1 A Feast for Crows, Chapter 14, Brienne.
- ↑ A Dance with Dragons, Chapter 71, Daenerys.
- ↑ A Dance with Dragons, Chapter 41, The Turncloak (Reek V).
- ↑ A Feast for Crows, Chapter 43, Cersei, p 801.
- ↑ A Feast for Crows, Chapter 43, Cersei, p 802.