Stefan Nagy
Yes, this is a school.

The quite strange acronym stands for "BundesGymnasium und bundesRealGymnasium", the eight stands for the 8th district of Vienna. "Bundes-" means that it's a state school, "Gymnasium" and "Realgymnasium" are the school types.

I marked the boundy of the school and tagged it with amenity=school, see https://www.openstreetmap.org/way/548204712