Spam is unsolicited commercial communication, most commonly in the form of email contact with the recipient.  Spamming is a distinctly electronic phenomenon as it is would be be prohibitively expensive to send out mass mailings via physical mail in the same fashion.  In the case of electronic spamming the cost is almost entirely borne by internet service providers and end users with next to zero cost for the spammers themselves–thus it remains profitable to send tens of thousands of spam emails and receive only one or two replies.

Modern email services like Gmail, Yahoo! Mail, and Hotmail include advanced spam detection algorithms to help reduce (but, unfortunately, not eliminate) the amount of Spam end users encounter.

For more information about Spam and Spam prevention techniques, check out the following How-To Geek articles:

• Does Email Address Obfuscation Actually Prevent Spam?
• Protect Your E-mail Accounts from Spam with Spamavert
• HTG Explains: How Scammers Forge Email Addresses and How You Can Tell