What is stomping??

New to Howrse so still figuring it all out!

Currently trying to collect all the coat colours for my favourite horses on here;

Arabians

Lipizzans

Pure Bred Spanish horses 

Percherons

I am breeding and trying to increase GP on all my foals the Lipizzan breed in particular!

Also focusing on building and improving my equestrian centre 

Any tips or support are greatly appreciated and I'll always try to return the favor! Returning all congratulations I see :)