1) the members:
people who arrive, register and post as well as reply.

they break down into several sub categories:

a.) wide open:
these folks come, write and read a lot. upload avatars, include their aim address, support others, and want to belong to the community.

b.) on the down low:
these folks will rarely start a thread, but often comment. they choose to be hidden from any who, or member list, and don't include avatars, or personal information about themselves.

c.) needy-nancy:
ubiquitous and often unhappy, these types are staccato and usually very annoying. they come, and begin slowly, but eventually start spamming your forums with personal things, links, hotlinked images, and drone about how lonely they are and how much they "love you guys." This person doesn't have real boundaries, or much sense of how they effect a community. Often they can become so obsessive that all other activity drops off completely until they are spoken to, curtailed, or banned.

d.) the troll:
someone who is either a banned needy-nancy, or former member who has hard feelings, or they are members with an opinion (usually malicious, but stated as humor) which they are not able to say as themselves. So they make false identities to slap or mock others for "fun."

2) the users:
People who are not interested in "joining," rather, they have a support issue and want to make use of the forum to get an answer. "where's my order?" or "how did you do that?" are often the questions a user will ask.

3) the readers:
some are members, others are not. they rarely, or never post. but they do aim you, email you and others about what they have read. good to have around, but in terms of a community forum, dead weight.