As ethicists, we are not interested in detailed descriptions of sex acts (there are other website where you can find that sort of thing). However, it is a good idea to know what we are talking about.
'Sex' often refers to intercourse, and for many people (such as a Christian teenager commited to remaining a virgin) this is an important distinction. There are people who have engaged in a variety of sex acts such as oral sex, possibly with a number of different partners, who would still call themselves a virgin. In fact, some churches have very specific criteria for 'what counts as sex'.
I don't think such distinctions are helpful - you can end up with a definition where a girl who has been raped is no longer a virgin, and a sexually active lesbian is. There are of course good reasons in law to be specific about what constitutes an act of sex (for example to be clear in cases of alleged sexual abuse). When we dicuss the ethics of sex, we're not really focussing on definitions. We are interested in the issues that sex and relationships raise.
In the issues section, we talk about masturbation. Many couples engage in mutual masturbation, but for the purposes of the discussion, 'masturbation' refers to masturbation by oneself.
When we talk about active homosexual relationships, we have not attempted to be specific. We do recognise that there is a difference between a gay couple living together but remaining celibate, and a couple who have an active physical relationship.
