Overloads

You might see the word "overload" in relation to functions, this is function overloading. It basically means depending on the parameters you pass, the function may do different things (i.e., returning a different type, interpreting the parameters differently).

In the case of ARController:GetCanvas(), it is used to outline the fact ARController:GetCanvas("3D") returns a WorldModel, whereas ARController:GetCanvas("2D") returns a Folder.