I have heard about things like \"C Runtime\", \"Visual C++ 2008 Runtime\", \".NET Common Language Runtime\", etc.
The runtime or execution environment is the part of a language implementation which executes code and is present at run-time; the compile-time part of the implementation is called the translation environment in the C standard.
Examples:
the Java runtime consists of the virtual machine and the standard library
a common C runtime consists of the loader (which is part of the operating system) and the runtime library, which implements the parts of the C language which are not built into the executable by the compiler; in hosted environments, this includes most parts of the standard library