The .NET framework provides several core run-time services to the programs that run within it – for example exception handling and security. For these services to work, the code must provide a minimum level of information to the runtime. i.e., code executing under the control of the CLR is called managed code. For example, any code written in C# or Visual Basic .NET is managed code.
Code that runs outside the CLR is referred to as “unmanaged code.” COM components, ActiveX components, and Win32 API functions are examples of unmanaged code.