Spam was originally SPAM, a brand of canned meat. There are many explanations for the origin of the brand name. The official version says that it is "Specially Processed Assorted Meat".

This SPAM meat was very popular for a while, to the point that it was everywhere and annoying. Later (in 1970), the Monty Python troupe had a very popular Sketch comedy (a short series of comedy) called Spam. In the play, two customers tried to order a breakfast without SPAM, but failed. So, many years later, Spam was used to refer to the phenomenon of spreading junk advertising messages everywhere on the Internet