A rabbit hole, in a metaphorical sense, is a long and winding exploratory path with many connections and offshoots.
The term rabbit hole is often used to describe online activities. The Web was essentially designed to function as a rabbit hole because of the way hyperlinks work, and Web surfing in general can be considered a voluntary trip down the rabbit hole. More purposeful examples of activities that tend to follow such paths include Web analytics, data analytics and various types of research. Interactive voice response (IVR) systems and help desk calls are among the other types of rabbit holes that people enter intentionally, if somewhat reluctantly.
In a fall down the rabbit hole, an individual sets off on the path with a goal, gets sidetracked by various events and changes direction several times along the way, eventually ending up somewhere unexpected, typically without having satisfied the original purpose of the quest. Nevertheless, the path often leads to serendipitous discoveries. Furthermore, according to the principle of obliquity, the meandering path may eventually turn out to be more productive than a more direct one.
The term rabbit hole comes from Lewis Carroll's "Alice's Adventures in Wonderland," in which a young girl called Alice falls down a rabbit hole, encounters many strange creatures and has many surreal experiences.