what is the "nested" means in C# IL

Hi @兰树豪 , Welcome to Microsoft Q&A,

In the context of C# Intermediate Language (IL), "nested" typically refers to a construct where one entity (such as a class or a struct) is defined within another entity. For instance, a nested class is a class that is defined within another class. Similarly, a nested struct is a struct defined within another struct, and so forth.

When you examine IL code, you may encounter nested types represented in the IL instructions. The IL instructions will reflect the structure of the code, including nested types. These nested types can have access to the members of their enclosing types (outer types), which can be useful for encapsulation and organizing related functionality.

The most intuitive way is to check the official documentation mentioned by Olaf Helper.https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/nested-types