> The common definition of a virgin is someone who has not had sex with a member of the opposite sex yet. Even this definition falls flat, though, when you realize that for many years, this was a physical issue, almost a medical one. A woman with an intact hymen was considered to be a virgin, and that was the end of the matter. Women in the Middle Ages, for example, were considered to be virgin if their hymen was intact. If a woman stretched or tore her hymen while horseback riding, she was simply and plainly no longer a virgin. If a woman was born with a tiny or nonexistent hymen, she was not a virgin.
It's also important to realize that there are still cultures today...

> This can seem strange to us, but it's important to keep in mind why the state of a woman's hymen was considered to be so vital -- it was the means by which one could prove that she had had sex with a man. A woman who had torn or stretched her hymen was "less valuable goods" (yippee for us, eh?) because her untouched state could not be determined with absolute certainty. A woman with a tiny or nonexistent hymen was similar. Thus a virgin was a woman who, it could be positively proven by physical evidence, had not had a penis inserted into her vagina.

http://www.io.com/~wwwomen/sexuality/virginity.html

And why was her 'untouched state' so important? Because in the days before paternity tests it was a way of being fairly sure that she wasn't already pregnant with another mans child.

(Though of course one can become pregnant without penetration breaking the hymen but I guess it is a lot less likely)

I call the penis-in-vagina sense of sex the 'Clinton definition' (for obvious reasons)

;-)