Netiquette is "Network Etiquette", a set of rules that we think should be adhered to to keep our community friendly, fair and respectful of the opinions of others. These rules range from the simple (do not post enormous pictures, as not everyone has a screen as large as you), to the practical (do not quote a message if your reply ends up immediately next to it as it wastes screen real estate and fills up our databases) to rules we impose, such as no commercial activity in our Technical Manual or our boards except for in the designated forum. Mostly, and common sense too:

• Read the Forum for a while before you post anything. This helps you to get an understanding of the culture of the group.
• Do not blame the system administrator for the behavior of the Forum users.
• Consider that a large audience will see your posts. That may include your present or your next boss. Take care in what you write. Remember too, that this Forum is frequently archived, and that your words may be stored for a very long time in a place to which many people have access.
• Assume that individuals speak for themselves, and what they say does not represent their organization (unless stated explicitly).
• Messages and articles should be brief and to the point. Don't wander off-topic, don't ramble and don't send mail or post messages solely to point out other people's errors in typing or spelling. These, more than any other behavior, mark you as an immature beginner.
• Subject lines should follow the conventions of the group.
• Advertising is abhorred on our Forums! Unsolicited advertising which is completely off-topic will most certainly guarantee that you get a lot of hate mail.
• If you are sending a reply to a message or a posting that is a number of messages removed from your reply you may quote parts of the original at the top of the message, or include just enough text of the original to give a context. This will make sure readers understand when they start to read your response. Giving context helps everyone. But do not include the entire original!
• If you should find yourself in a disagreement with one person, make your responses to each other via mail rather than continue to post on the Forum. If you are debating a point on which the group might have some interest, you may summarize for them later.
• Don't get involved in flame wars. Neither post nor respond to incendiary material.
• Avoid sending messages or posting articles which are no more than gratuitous replies to replies.
• Be careful with monospacing fonts and diagrams. These will display differently on different systems, and with different mailers on the same system.

If you'd really like to know about formal netiquette, there is a formal standard for it, RFC 1855. If in doubt, please read that.