The writers of "The Ethical Slut" advocate for a very broad definition of having sex. They even have a (tongue-in-cheek) bit where they say that by reading the book, you and the authors are engaging in a form of having sex.

I'm not sure I totally agree with going that far, but I do think a broad definition is better.

Nah any sex is losing your virginity

I'll take it in another direction from the other responses and just say: people give too much of a fuck about this idea of virginity.

I'd say as long as it involves another person it counts.