How do lesbians lose virginity?

It just occurred to me that in a sense I really am a virgin. After all, I have never been with a woman. Does anyone knows what lesbians consider losing their virginity. When can it be said that one has engaged in lesbian sex–officially? Always the standard for sex has been penetration but with lesbians that isn’t an issue–or is it? I don’t know because when it comes to lesbianism I am a virgin. I bet there would be a lot of people interested in knowing if I take the step to change this, and the process involved. Any thoughts?