Whats the difference between Magnetic & Crystal headphones?

I have an old tube tester which has a jack labeled "NOISE"
I downloaded a manual for it and it says that is to hear noisy tubes.
Then it says use MAGNETIC headphones, crystal headphones will NOT work.

I wont likely ever use this function, but I am curious......

My guess would be "magnetic" phones would have something like a speaker
in them, and that all modern phones are made this way. (just a guess).

So what is a crystal headphone and how does that work?