What does sidechain on Delay do?

I am familiar with compressor sidechain.
You send the signal to a compressor and the signal set treshold for the compressor.

But with the delay’s sidechain alone without compressor how does it work?

Thank you.

It acts as ducking delay

You can use an audio source to trigger when the delay does or does not do it´s thing.
Watch this, it will explain better than me.

https://www.youtube.com/watch?v=iqZEVZnsyJ8

Nice one! I saw this too, a little more detailed explanation.