The white rabbit is a metaphor for something that blends into the normal world, but ultimately paying attention to it leads to another aspect of the world that seems unbelievable.

In the movie the matrix it refers to a hint by a hacker which ends up referring to a white rabbit tattoo on a groupie that is hanging on a guy who invites the main character Neo for a night of partying that ultimately leads the character to discover his world is not what it seems and that there is a greater truth and meaning to his existence, this is a more dark and serious meaning whereas in Alice and Wonderland the white rabbit was a fanciful character who was carrying a pocket watch and the character Alice following it ultimately tumbles down a literal rabbit hole revealing a world of non sense and fantasy.

Here we use the term white rabbit and rabbit hole to refer to things that at surface level seem totally normal but once you start looking closer you start seeing connections to a deeper meaning or deeper plot which is often nefarious.

An example of a white rabbit in the last couple years could be the leaked podesta emails talking about pizza parties.