Runtime environment
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A runtime environment is software that provides a layer between an application and the operating system. For example, programs written in Java, run in the Java Runtime Environment. And programs written in C#, Visual Basic .NET, C++ .Net, and so on, are run in the Microsoft .NET Common Language Runtime (CLR) for Windows or Mono for Linux. Applications written for a particular runtime environment can theoretically be run, without recompiling, on various platforms.