User blog comment:HiddenVale/Enlighten me, please/@comment-452-20121001030909

Spam is a catch-all term for anything unwanted.

The origin of the term is from Monty Python's Spam sketch, where a group of Vikings are constantly singing about Spam (The canned meat product) very loudly, and drowning out the person speaking.

The earliest uses of the term "spam" online was the same as the word "flood", which meant repeating something in order to drown out everyone else, just like in the original sketch.

Today, possible uses of spam include:
 * Flooding
 * Advertising
 * Inserting gibberish
 * Cross-posting the same message in multiple places

Most people's definition of the word is vague, so the only thing you can "rely" on is that "spam" means something unwanted.