Virginity

Cordelia: “Why is it always virgin women who have to do the sacrificing?”

Wesley: “For purity, I suppose.”

Cordelia: “This has nothing to do with purity. This is all about dominance, buddy. You can bet if someone ordered a male body part for religious sacrifice the world would be atheist like that.”

— Cordelia Chase and Wesley Wyndam-Pryce

Virginia Bryce, being offered to the demon Yeska under the false belief that she was still was a virgin.

Virginity was the state of a person who has never had sexual intercourse, a virgin being the term for an individual who retained their virginity. Several spells required the ritual killings of human virgins, and many demons fed on or accepted virgins as offerings (particularly females), due to their perceived purity.
Kleptes-Virgo, meaning virgin-thief, referred to a group of different mythical creatures from various ancient cultures that preyed on male virgins by assuming the form of their female counterparts and seducing them.

Demons

• The Invocation of Machida required a live offering of three female virgins to said demon in order to gain the riches it offered.
• Davric Demons offered great magical power to their human worshipers if they presented them with a virgin sacrifice to feed on during the person's fiftieth birthday.
• Vampires seemed to enjoy the blood of virgins.
• Eli was executed by Angel for dismembering virgins for his own enjoyment.

Rituals and spells

• The Shroud of Rahmon was said to have been dyed in the blood of seven virgin women after it was woven.
• By applying the blood of a freshly killed virgin on Cordelia's stomach, Connor expedited the birth of their unborn child.