Common Language Infrastructure
Created by Microsoft as the foundation of its .NET technology, the Common Language Infrastructure (CLI) is an ECMA standard (ECMA-335) that allows applications to be written in a variety of high-level programming languages and executed in different system environments.
Programming languages that conform to the CLI have access to the same base class library and are capable of being compiled into the same intermediate language (IL) and metadata. IL is then further compiled into native code particular to a specific architecture.
Because of this intermediate step, applications do not have to be rewritten from scratch. Their IL only needs to be further compiled into a system's native code.