What does AeroSpike engine work?

I have just wondered and confused.

( I saw it in right here first time )[https://www.simplerockets.com/c/JXnZE2/Linear-AeroSpike-Engine-Stock]

Is it Ion engine or Heated Water engine( electrical rocket engine) ? What is its fuel?

I watched a video but my English is bad and youteber talked too fast and I didn't catch some words. Sooo I confused.

( Video is here )[https://m.youtube.com/watch?v=qT9HBkWGg7s&list=WL&index=17&t=279s]