Q: How to connect Mac products?

Hey guys,

Okay so I've seen my teacher do this and I was wondering how to do it:

Basically he runs a presentation on his iMac and then controls it on his iPhone wirelessly that also has the presentation up. I'm not talking about connectors etc like USB, VGA, thunderbolt etc

I think it's an app but I'm not sure and obviously with it being college holidays I can't ask him yet. Any help would be much appreciated! Thank you very much!