Question about type or namespace error

C# Error CS0234 – The type or namespace name 'name' does not exist in the namespace 'namespace'

The type or namespace name 'AddressableAssets' does not exist in the namespace 'UnityEditor' (build)

What is a namespace, and what does a module's namespace contain... | Filo

Exploring Namespace Structure

Building an Enterprise Unified Namespace to Power Your Smart Factory

How would you solve a namespace conflict in one of your classes... | Filo

C# Error CS0116 – A namespace cannot directly contain members such as fields or methods