These taps have a creamer disk so when the beverage is pushed through this disk at high pressure it will atomise the liquid giving your beverage a creamy head and a fine bubble that cascades in the glass. These are typically used for stout or nitro coffee however they are now starting to become popular for various other beers.
To get the most out of this tap you really want to use nitrogen. More information can be found here:
Recommended for the Stout Tap | Nitro Coffee | Stainless Steel