Commissioned officers are classified by their area of concentration, or AOC. Just like enlisted MOSCs, AOCs are two digits plus a letter. Related AOCs are grouped together by specific branch of the Army or by broader in scope functional areas (FA).
https://en.wikipedia.org/wiki/List_of_United_States_Army_careers#:~:text=Commissioned%20officers%20are%20classified%20by,scope%20functional%20areas%20(FA).
A Modification table of organization and equipment (MTOE) is an authorization document that prescribes the modification of a basic TOE necessary to adapt it to the needs of a specific unit or type of unit.Oct 31, 1999
https://fas.org/man/dod-101/army/unit/toe/toenum.htm#:~:text=A%20Modification%20table%20of%20organization,unit%20or%20type%20of%20unit.