An email bacn is a term coined at 2007 PodCamp in Pittsburgh. A bacn is a legitimate email for wich the recipient has signed-up but that is not read because of lack of time. During the Pittsburgh conference it has been simply defined as " an email you want but not right now".
It is not really an operational definition, but it has the merit to emphasize on all legitimate email messages that most often are no longer read and on increasing email volumes sent by merchants and other companies.
A bacn, pronounced like bacon, is not to be confused with an email beacon
See also spam and ham messages.
Image credit Bacn2.com