Yesterday, I took a crack at defining engagement, and along the way covered lurking, interaction, and participation. These are the initial steps on the way to building and sustaining vibrant online communities, as illustrated in David Armano's Marketing Spiral.

The last two phases of creating community are conversation and affinity.

Conversation
This is what happens when people who are interested in the same thing start talking to each other. Conversations happen when participation becomes social. Participation requires us to contribute our ideas and content; conversations are the result of those original thoughts running into and being influenced by other people's thoughts. It's a cyclical process that creates an ongoing series of interconnected blog posts, message board posts, twitter messages, videos, and photos.

Affinity

Affinity is where [our shared interest] transforms, yet again, into something deeper. Something personal. Where the link between the brand and the consumer (or the brand and my sense of self) intertwines. - Gavin Heaton

Fortunately, Gavin left this brilliant gem in the comments yesterday. I think it sums things up perfectly. Affinity is the culmination of our shared experience with the other members of the community, in which being part of the community becomes part of our own self-identity.

Now, I guess I'm going to have to define community...