Disgaea Wiki
Defending State

Since Disgaea 3, Defending units have a special indicator above them.

Defending is one of the basic actions that units can perform in battle, activated through the "Defend" command. This puts units in a special state where they can't act or move, but take decreased damage. The command can be cancelled at any time during your turn, unless the unit has been attacked. Once a unit ends the turn while Defending, the state will remain until the start of their next turn.

When a unit is Defending they take 50% less damage(changed to 25% in Disgaea 7) and their remaining amount of counters is decreased by 2. Since Disgaea 5, Defending also grants a 25% evasion chance. In games up to Disgaea 5, starting a turn in Defending state also cuts Poison damage taken in half.

In Disgaea 4, if a Defending unit is targeted by an area attack, an adjacent ally standing behind them(from the point of view of the attacker) will not be affected by the attack.

Defensive classes like the Armor Knight (Male and Female) often have Evilities that improve Defending or grant it additional effects. The Female Armor Knight's recurring "Galahad's Shield" skill puts her in Defending state on top of dealing damage, however unlike with the basic command the state can't be cancelled.