The jus primae noctis meaning 'law (or right) of the first night,' and droit du seigneur meaning 'the lord's right', is the purported right of the lord of an estate to deflower its virgins.
Although referred to in 16th century literature, examinations of records by historians have found no evidence of its existence in mediæval times. In some feudal systems the culagium was imposed by the local lord: a requirement that a peasant get permission to marry from his lord, which often involved a fee. Ecclesiastical authorities in some regions also demanded a fee before a new husband was allowed to consummate his marriage with his wife. The right of the first night, however, is unlikely to have existed and is probably a distortion based on these.
In the 16th century Boece referred to the decree of the invented Scottish king Evenus III that "the lord of the ground sal have the maidenhead of all virginis dwelling on the same." Legend has it that Saint Margaret procured the replacement of jus primae noctis with a bridal tax. King Evenus III did not exist, and Boece included a lot of other material in his account that was clearly mythical.
Also, in Terry Pratchett's novel Wyrd Sisters, the droit de seigneur is referred to when Duke Felmet (then monarch of the Ramtop kingdom of Lancre) failed to find anyone who is prepared to explain the concept to him, and thus assumes that a droit de seignur is a kind of large, hairy dog that needs exercise every so often.
Reference
Boureau, Alain, The Lord's First Night: The Myth of the Droit de Cuissage, trans. Lydia G. Cochrane, University of Chicago Press, 1998. ISBN 0226067424
External link
The Straight Dope: Did medieval lords have "right of the first night" with the local brides? (http://www.straightdope.com/classics/a5_181.html)
The custom of someone other than the husband being the first to engage in sexual intercourse with a bride after the wedding (and thus being the one to relieve her of her virginity) goes back several thousand years and is tied to the concept of God as the source of all life.
[The droitduseigneur] is paralleled in various primitive societies, but the evidence of its existence in Europe is almost all indirect, involving records of the redemption dues paid by the vassal to avoid enforcement, not of actual enforcement.