What’s the difference between London St Pancras Domestic and London St Pancras International?

I'm travelling in the UK if thats any help.

domestic

national rail so you can to other stations in north London and the rest of northern England

London underground is in the domestic bit so you can connect to different places on the underground system in London

international

for the euro star so you can get trains to Paris and other cities across Europe (in the European union)

hope this helps

Ian M