I've found this phrase appears more than twice. Ted-ed at 1:15
So, to use matrices, we need to learn how they work. It turns out, you can treat matrices just like regular numbers. You can add them, subtract them, even multiply them. You can't divide them, but that's a rabbit hole of its own. Adding matrices is pretty simple. All you have to do is add the corresponding entries in the order they come.
What does rabbit hole mean? How to use it? Could you please give me some examples?
Best Answer
Rabbit hole commonly refers to either an actual rabbit burrow where rabbits live, or, as an idiomatic phrase used in your Ted-Ed example, the hole Alice went down following the white rabbit in Alice in Wonderland. It metaphorically describes something unknown, possibly fantastical, that will lead to much more complexity than it initially appeared.
In the video he is using rabbit hole to humorously state that the reason for no matrix division is beyond what he can cover in a 4'40" long video. He is giving a top level description of mathematical matrices to an audience that is unlikely to be familiar with the concept. You can add, subtract, and multiply matrices, but you cannot divide them.