CIL - Common Intermediate Language
The language all .NET languages compile to. Equivalent to Java bytecode.
CLI - Common Language Infrastructure
The combination of the CLR, CLS, CTS and CIL
CLR - Common Language Runtime
The runtime environment itself, including garbage collection, threading etc.
CLS - Common Language Specification
A set of conventions intended to promote language interoperability.
CTS - Common Type System
The language-neutral type system used in the CLI.
IL - Intermediate Language
More commonly used abbreviation for CIL.
VES - Virtual Execution System
Another name for the CLR as far as I can tell.