00 = Command: Delete, Garrison, Stop | Attribute: Hit Point
01 = Animal
02 = Non-Military Building
03 = Villager
04 = Military Unit
05 = Trading Unit
06 = Monk
07 = Transport Ship
08 = Relic / Monk with Relic
09 = Fishing Ship
10 = Military Building

This slot affects which command(s) the unit will have and which attribute of it will be displayed (when the unit is selected).

2 and 10 can only be used by buildings, they control which list the building's build command button would appear on as well.

credit to Trisolo/scenario_t_c