Bacn is email you asked for — shop newsletters, airline deals, notices from a service — but you do not really want to read it right now, or maybe ever. It is not a stranger pushing junk at you. You clicked “subscribe,” so the mail is allowed; though actually it still fills the inbox, and many people skip it the way they skip spam. The word is a joke from internet people in 2007, at a meeting called PodCamp Pittsburgh 2: spam is the meat you never ordered, and bacon is the meat you like even if you cannot eat it all at once. So bacn sits between a real letter from a friend and true junk. It is informal tech slang. Most people still just say “newsletter”; you will not hear bacn at the dinner table.