Spam
Spam is unsolicited e-mail. It is often commercial in nature and may contain viruses or other malware.
Legitimate, non-spam e-mail is sometimes called ham.
Preventing
The best way to protect yourself from receiving spam is to never give out or publish your e-mail address.
If you ever need to sign up for something online with your e-mail address, make sure to review the website's privacy policy and if possible, opt out of any solicitation or information sharing.
Controlling
Some e-mail clients like Apple Mail and Mozilla Thunderbird offer built-in spam detection.
鶹Ƶ offers server-side spam control through a program called SpamAssassin. The page offers a web-based interface to configure SpamAssassin.