source - http://stackoverflow.com/a/2617483
Full trust - your code can do anything that the account running it can do. High trust - same as above except your code cannot call into unmanaged code. i.e. Win32 APIs, COM interop. Medium trust - same as above except your code cannot see any part of the file system except its application directory. Low trust - same as above except your code cannot make any out-of-process calls. i.e. calls to a database, network, etc. Minimal trust - code is restricted from anything but the most trival processing (calculating algorithms).
origin - http://www.pipiscrew.com/?p=3501 asp-net-trust-levels