I am not sure if this has a particular name, but I am thinking it might, because I see it a lot on modern bridges and tall towers that serve as tourist attraction. What is it called, is there a name for such a thing?
This kind of tourist attraction is often called a "glass observation deck", or sometimes just an "observation deck", although there are also observation decks without a glass floor.
If you have a glass floor in some other context, I'd just call it a glass floor, or maybe a glass deck if it's outdoors.
The most general, basic term for that, is glass floor.
Sometimes, the term for something is just simply calling it what it is. In specific instances, a different term might be used, but they are limited to specific situations.