E-mail spam, also known as junk e-mail, is a subset of spam that involves nearly identical messages sent to numerous recipients by e-mail. A common synonym for spam is unsolicited bulk e-mail.
Three Major Types of Spam
Attempts to infect your computer. These emails typically ask you to open an attachment which causes the infection, or take you to a website where the infection is downloaded.
Product sales. These are trying to entice you to buy drugs, body enhancement aids, jewelry or the like at enticingly low prices. The problem, of course, is that most are scams, or the drugs are outdated, the aids don't work and the jewelry is fake.
Phishing attempts. These are trying to entice you to provide your personal information by imitating some other legitimate site with which you may have an existing relationship. Once you give up your personal information, identity theft and credit card fraud follows.