Slang of backpacking through Europe, often in reference to jumping from country to country in search of alcohol and intercourse.
Because the countries of Europe are essentially 2 hours apart from each other. Many young (or old) non-Europeans seek to travel or backpack through Europe in search of adventure, getting wasted on euro booze and having one night sexual relations with european persons.
Person A: Bro, remmember when we were talkin about euro hopping?
Person B: Dude! Fuck yeah, let's go, bro!
Person A: iiight, we'll hit up Germany first, drink their kick ass booze, then we'll hit up Belgium and bang some ridiculously hot chicks.
Person B: awesome, then we'll go to France and make fun of French people