In these communities, virginity is expected of women until marriage, at which point they are only allowed to have intercourse with their husbands. Historically, this was used to control and ensure the lineage of children for inheritance purposes, but has no real legal significance today.
While female virginity is seen as a virtuous, male virginity is often mocked and ridiculed in North American culture. Male virgins are seen as un-masculine, socially inept and undesirable, and must remedy this "lack of worth" by having sex as soon as possible.
Religious beliefs and culture greatly influence one's view of virginity. More liberal cultures tend to not expect female virginity before marriage.