Getting caught up in a seemingly endless loop of internet content, typically started by a youtube video or wikipedia entry. The user continues to look up even slightly related content, spiraling from related topic to related topic, typically losing hours out of the day.
Can also be used as a verb "to internet spiral."
Justine ended up in a deep internet spiral after Jess sent her a link to an old Bruce Springsteen video on youtube.
Jess internet spiraled her entire Sunday away looking at pictures of lolcats and other hilarious content.