Guide to the Godot game engine/Global scope
The GlobalScope is where all the more... Global... Methods and constants are. These include math functions like sin and cos. It also has random number generators, such as randi.
See Godot's documentation for more: https://docs.godotengine.org/en/latest/classes/class_@globalscope.html and: https://docs.godotengine.org/en/latest/classes/class_@gdscript.html
Do not confuse it for keywords.