You can read this Wikipedia article, Managed Code . Mostly managed code is Microsoft's term, but the concept is not new. Consider the following definition :
An application program executed as part of an execution engine installed on the same computer. The application cannot work without it. The runtime provides a common library of program routines that the program uses and typically performs memory management. It can also provide time-based conversion (JIT) from source code to executable code or from an intermediate language to executable code. Java, Visual Basic, and the .NET Common Language Runtime (CLR) are examples of runtime mechanisms.
Now compare this with the definition of unmanaged code:
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