CommandMethod
Short answer
The .NET attribute you place on a method to expose it as a typeable AutoCAD command after NETLOAD.
[CommandMethod("MYCMD")] is the C# attribute that registers a method as an AutoCAD command. After NETLOAD reflects over the assembly, the user can type MYCMD at the AutoCAD command line to invoke it. Variants set command flags ([CommandMethod("MYCMD", CommandFlags.Modal)]) or scope the command to a group. Most marketplace plugins ship dozens of CommandMethods grouped under a single global name prefix.