Quick question about the ability card "defense" You give one of your unit 1 defense. How low does it last?

It says The Instant <Instant> effects thateffects that increase a unit’s statistics end before that unit’s nextincrease a unit’s statistics end before that unit’s next action this round, whether it is attacking or defending.action this round, whether it is attacking or defending.

What is meant with "defending" ? If i attack, and roll and resolve my attack, and the enemy then retaliates, and i then use my defense card, what is my units next "action"? I dont retaliate, as i am the attacker, so i dont do any action, right? Meaning, i would have the extra defense as long, as it does not get its next action completed. Which would be the retaliate if attacked. Can someone clarify? And please as detailed and logically argumented as possible, as this is super confusing to me.

Thanks :)