A rabbit hole was a hole in the ground where rabbits lived.
In 2256, Michael Burnham quoted a passage from Alice's Adventures in Wonderland while crawling through a Jefferies tube on USS Discovery: "The rabbit hole went straight on like a tunnel for some way, then dipped suddenly down, so suddenly that Alice had not a moment to think about stopping herself, but instead found herself falling down a very deep well." (DIS: "Context Is for Kings")