Back when I was active on AVEN (I have no idea what it's like now), we had two definitions of asexual -- an external definition and an internal definition. The external definition, the one that's on the wiki and the press material and that everyone uses when talking about asexuality, was of course "an asexual is someone who does not experience sexual attraction". The internal definition, the one we kept in mind when talking to each other, was "an asexual is someone who calls themself asexual".
The reason for this was very simple and very practical. In the very early AVEN and immediately pre-AVEN days, back before my time when the disparate ace communities were first finding each other and creating a public online network, there was a fair lot of exclusionist discourse. There are a lot of ways to be asexual, and the early community of course fell prey to the usual infighting about whether someone with a libido counts as asexual, whether someone who chooses to have sex can be asexual (usual tiring Purity Brigade Bullshit), whether someone without a libido counts as asexual (after all, if you have no sex drive, are you sure it's a matter of sexual orientation?), whether ace people count as lgbtq, all the usual nonsense. This worked out the way it pretty much always does -- the inclusionists "win", because exclusionists always break off into smaller and smaller communities so the largest group is, of course, the one where all different kinds of people stick together and welcome each other. And that was AVEN.
And when you're trying to have a strong community and somebody shows up at the gates saying, "hi, I think I'm asexual", it's a fucking horrible idea to start doubting their credentials. They saw the public definition and started calling themselves asexual; they're here, and now they're under the internal definition. An asexual is somebody who calls themself asexual. Sometimes, these people would be frustrated allosexuals, or people choosing to swear off sex, who might not fit the external definition of the term. We made sure that everyone knew the external definition, and there were always conversations about asexuality and how it affected our lives, if they asked us directly what we thought then we'd say "only you can know for sure" and then give our thoughts on the matter for as long as they asked for them, and other than that it wasn't anyone else's fucking business or anyone's place to judge. If people weren't nasty and didn't create problems, they could stay and call themselves whatever they wanted.
Many of these people who didn't fit the strict definition eventually left after receiving support and discovering more about themselves. Some stopped IDing as ace but became allies to the community. Some people who came in with the most "I'm a heterosexual girl who is angry at my boyfriend" intro posts you've ever seen in your life discovered that they were in fact ace and that the messages that society had taught them about sex and romance were simply not for them -- these are people who, in a gatekept community, would have been incorrectly ousted immediately.
And then there were people -- a LOT of people -- who found themselves in grey areas. People who said "okay, this community makes sense to me and is useful to me and I have so much in common with a lot of you, but not EXACTLY like you. However, what I experience may not be the strict default definition but it's an awful lot like these other members on the forum." And they formed sub-communities. The grey aces. The demisexuals. The aromantics and greyromantics. Through these dialogues, between subgroups who in a more exclusionary community would be arguing about who the "real" asexuals are and splintering off into their own communities away from all those stupid cishet fakers, we developed language to describe our similarities and differences. The sexual/romantic/aesthetic attraction model came out of these dialogues and it became so massively important to our understanding of asexuality that basically everyone in the ace/aro community describes themselves by it, as do a large number of people outside the community. The community made massive leaps ahead in just a decade or two by, well, being a community. By being a place where anybody who called the place home, and didn't bully other people in the home, was right. By being somewhere where anybody who saw "asexual: someone who doesn't experience sexual attraction" and thought "that sounds like a term with some use for me" was allowed to use it.
An asexual is somebody who does not experience sexual attraction.
An asexual is somebody who calls themselves asexual.
These definitions are not in conflict -- they are both, in concert, fundamentally necessary for a safe and vibrant community where we can protect, support, and learn about each other and ourselves.
And that is absolutely not exclusive to asexual communities.
