[The Go to Definition function] will show what the public definition of the type or member looks like by reading the metadata in the compiled assembly. Some tools, such as ILSpy .NET Decompiler, will even reverse-engineer from the metadata and IL code back into C# for you.
First of all, I would say that C# is a a programming language. Why does it say: "back" into C#? Does it mean that: there are some tools that return some data for you by the c# language?