Microsoft.NET Question:

CLR
See definition for common language runtime.
CLS
See definition for Common Language Specification.
common type system
The specification that determines how the common language runtime defines, uses, and manages types.
common language runtime
The engine at the core of managed code execution. The runtime supplies managed code with services such as cross-language integration, code access security, object lifetime management, and debugging and profiling support.
Common Language Specification (CLS)
A subset of language features that is supported by a broad set of compliant tools. CLS-compliant components and tools are guaranteed to interoperate with other CLS-compliant components and tools. See also: CLS-compliant.