Spam (when it’s not being used to describe a meat product) usually refers to junk or bulk emails delivered without permission to a person’s email address. The term is sometimes applied to the attempt to artificially elevate the PR of a site on a search engine – in other words, the use of Black-hat techniques, or Cloaking.
E-mail spam has grown exponentially and now averages more than 90% of all e-mail sent. In April 2008 more than 100 billion spam emails were sent per day. According to some sources, about 80% of all spam is sent by fewer than 200 spammers.