The term "rabbit hole" is an idiomatic expression that refers to a situation or circumstance that leads someone down a path from which it may be difficult to return. It can also refer to something that seems simple and innocuous on the surface, but actually has deeper implications or consequences.
In its most famous use, "rabbit hole" is a phrase used in reference to Alice's Adventures in Wonderland by Lewis Carroll. In the story, Alice falls down a rabbit hole into an imaginary world filled with strange and fantastical creatures. The term has since become synonymous with entering into something that is difficult to understand or navigate.