Depends who you ask:
Maintenance Incident Report (RoyalAustralian Air Force)
Management Information Report
Management Information Repository (Sprint)
Mandatory Inspection Requirement
Maryland International Raceway
Master Inventory Record
Material Inspection Report
Material Investigation Report (GTE Services)
Maximum Information Rate (ATMF)
Medical Inspection Room
Micropower Impulse Radar
Microwave Imaging Radiometer
Mid Infrared
Mishap Investigation Report
Missile Intercept Report
Mission Integration Review
Monastir, Tunisia - Skanes (Airport Code)
Multiple Instructor Requirement