Primary Attack
The main attack of your unit. Every unit has one.
The primary attack is not necessarily the first attack that a stack does in a battle: if your unit also has an Extra Attack, and that is of higher Initiative, that one is done first.
A Primary Attack causes enemy units to attempt to Counter (even if it fails due to being paralyzed, too far away, or 0 Attack Power Counter).
Using a Primary Attack will cause Fatigue to your unit, which is a reduction in Efficiency.
Primary Attacks are affected by Attack Power Boosters/Diminishers, Accuracy Boosters/Diminishers, and Efficiency Boosters/Diminishers. The Primary Attack's type affects unit behavior when it is on the ground. For example, an Earth Elemental might ignore a Flying stack in favor of one on the ground, if the ground stack is large enough and the elementals are also on the ground.