MI is Military Intelligence.
ADSO - Active Duty Service Obligation. This refers to a program currently in effect in the Army that allows USMA and ROTC cadets to extend their ADSO by 3 years for their choice of branch, post and/or grad school.
For instance, if a USMA cadet really wants Infantry but ranks too low, he can get it by adding 3 years AD on his commitment. The new commitment would be 8 years AD as opposed to 5 years AD and 3 years reserve.
In my post above 109 cadets selected aviation. Of those 109, 19 of them had to get it by extending their ADSO by three years. This three years is on top of the USMA commitment plus the flight school commitment.