Some definitions of spam indicate that the messages are for the purpose of commercial advertising, which is for the most part true, but not always. The term was first associated with Usenet, and was later adopted as a term for floods of duplicate e-mail messages. E-mail spam lists are often created by scanning Usenet postings, stealing Internet mailing lists, or by searching the Web for addresses.
Directories are another source of e-mail addresses.
The more Internet activity you participate in, the more likely you'll end up in a spam list. Delete the message. Think of it in the same context as throwing away the junk mail you receive at home. This can inadvertently cause all original addressees to receive the reply, causing another flood. Mailing lists can explode into thousands of recipients.