Originally Posted by travelnutz

On some trains, there are "guaranteed" seats in the sense that your seats are reserved. These trains are usually fairly new Eurostar trains. BTW, if you have a chance to ride one, it's a great experience! On those, you are given a specific seat on the train. On other non-Eurostar train, you have a seat but it's not any specific seat. Those are usually smaller, regional trains where it's first come first serve and the difference between 1st and second class is even more blurry.