The back of the photograph says "Ostend Station", but this is a tram heading towards the former (second) station and not the current one.
None of the buildings visible in the background still exist today: https://maps.app.goo.gl/cKTZDdSaPM1UfqMT6
The photo was taken on one of the busiest days of the year, explaining the three additional trailers.
Since the tram is empty and there is no line number visible at the front, it can be assumed that the tram came from the depot.
The trailers are also a chapter unto themselves: each trailer on this photo is different. It's impossible to speak of a uniform set here...
The history of the trailers is quite complex and requires a lot of research, especially because there have been many renovations and renumberings.