Detailed article in Microsoft Docs

XML documentation comments are a special kind of comment, added above the definition of any user-defined type or member. They are special because they can be processed by the compiler to generate an XML documentation file at compile time. The compiler-generated XML file can be distributed alongside your .NET assembly so that Visual Studio and other IDEs can use IntelliSense to show quick information about types or members. Additionally, the XML file can be run through tools like DocFX and Sandcastle to generate API reference websites.