On a travel day (00.00-23.59 CE(S)T), you can board as many trains as you like, so a round trip Brussels-Brugge during one day will be fine.

It depends on the specific terms and conditions of your pass. If your pass includes unlimited travel for a certain number of days, then yes, you can typically use it for a round trip between two cities in one day without it counting as two separate travel days. However, if your pass is based on a specific number of travel days, then each day you use it for travel, even if it's just a round trip between two cities, counts as one of your travel days.

However, if you have a pass that is based on a certain number of travel days, such as a flexi pass, then a round trip from Brussels to Bruges and back would typically count as two travel days, even if you complete the trip on the same day.

That is NOT correct. Where did you get that information from?

On a travel day (00.00-23.59)  no matter if it is a continuous pass or a flexi pass,  you can board as many trains as you like. 

Hey Dear,

Yes, it is typically possible to do a round trip from Brussels to Bruges in a single day using a train pass or tickets, depending on the specific pass or ticket you have. The train journey between Brussels and Bruges is efficient and takes approximately one hour each way, making it feasible for a day trip.

You can catch a morning train from Brussels to Bruges and spend the day exploring the charming city, enjoying its historical architecture, picturesque canals, and local attractions. Bruges is known for its well-preserved medieval town center, so there is plenty to see and do. Do you want to require more information about it.

Yes, you can do a round trip from Brussels to Bruges in one day using your pass, as long as the pass covers travel within Belgium and allows for multiple journeys on the same day. I hope you understand it.

Does the pass cover all types of trains, including high-speed or regional ones, for the round trip between Brussels and Brugge?

 There are no high speed trains (tgv-like) between Brussels and Bruges, but only domestic NMBS/SNCB  services. You can take every train in Belgium of NMBS/SNCB, to wherever you’re going in Belgium. No seat reservations needed, not even possible to make.

Check timetables on https://www.belgiantrain.be/en . There are three direct trains per hour Brussels-Bruges, extra trains option during rush hours or holiday periods when people go to the coast.

@DesmondEdwin 

Unless you have enough days or a continuous pass, you could ask you it is really necesseary to use the pass between Brussels and Brugge.