Mono is a software platform designed to allow developers to easily create cross platform applications. It is an open source implementation of Microsoft's .Net Framework based on the ECMA standards for C# and the Common Language Runtime.
There are several components that make up Mono:
C# Compiler - The C# compiler is feature complete for compiling C# 1.0 and 2.0 (ECMA), and also contains many of the C# 3.0 features.
Mono Runtime - The runtime implements the ECMA Common Language Infrastructure (CLI). The runtime provides a Just-in-Time (JIT) compiler, an Ahead-of-Time compiler (AOT), a library loader, the garbage collector, a threading system and interoperability functionality.
source:http://linuxpoison.blogspot.com/2010/11/13578167754293.html