Internet term referring to a starting out following one link, which just leads you to another, than another eventually you are someplace bearing no resemblance to where you started. Sometimes you just have to stop following the rabbit hole because there is no end in site.
Rabbit holes are often followed as one link you visit gives you an idea to visit another link and the process just repeats itself endlessly.
Some people avoid rabbit holes at all cost, as the can be very time consuming and suck you in deeper and deeper.
Example: I recently followed a link on Reddit given to me by a friend from /r/counting that just kept getting deeper - that eventually lead to a conversation that has been ongoing for over 8 years and over 40,000 comments - that rabbit hole lead to another conversation with over 60,000 comments. In following those steps I have at least a dozen bookmarks to other conversations relating to those. I may never find the end of the rabbit hole!!
Brevity Quest 2016