what do the different level of corps unit AI mean?

[oho]

The title has it all 

[oho]

I mean the 3 levels of AI that I can chose in the bottom of the corps unit card...

[AJ]

Initiative I believe.  You can change the initiative of the Corp during the Battle

[oho]

Does this mean agressivness?

[oho]

anybody can answer the question?

[thilio]

Initiative I believe.  You can change the initiative of the Corp during the Battle

Agree.
It changes the initiative level of all the units of the corp.
Unit initiative from the manual p51: A unit with a large capacity for taking initiative will tend to react quite strongly to
various threats, which may compromise your battle-plans. Similarly, it will tend to pursue to the full an enemy unit in difficulty.