C# - Assembly unit

C# defines new translation unit of application composition called assembly unit. Microsoft MSDN website defines assembly unit in following way:

Assemblies form the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions for a .NET-based application. Assemblies take the form of an executable (.exe) file or dynamic link library (.dll) file, and are the building blocks of the .NET Framework. They provide the common language runtime with the information it needs to be aware of type implementations. You can think of an assembly as a collection of types and resources that form a logical unit of functionality and are built to work together.

In short, assembly unit is translation unit having some integral functionality compiled to one .dll or .exe file. In C# solutions assembly unit usually is one C# project or C# library.