Reference:
Data trees and C# in Grasshopper
GH_Structure and IGH_Goo Interface are two terms that appear a lot while I try to develop a Grasshopper Component. I’m trying to understand them in C#.
Definations from Grasshopper SDK Help
GH_Structure<T> Class: Represents a data tree where each branch has a unique path
IGH_Goo Interface: Base interface for all Data inside Grasshopper. Every parameter must implement a type of Goo.
John H. Holland
David E. Goldberg