IDL is a scientific programming language used to visualize data. MIDL is the Met Office IDL library, a series of functions for use with IDL.
Availability
Atmospherics managed Linux workstations only.
Instructions for users
To use regular IDL do
module add idl idl
To use MIDL
module add idl module add midl midl
Licence Details
This is proprietary licence managed software. CAS bought the licences so only their computers have access to the software.
Documentation
Source
http://www.harrisgeospatial.com/ and (presumably) https://www.metoffice.gov.uk/homepage.