What is it and how does it work?
Deloading is literally either taking a rest week or going lighter on weight for a week or two.
This is something that powerlifters use more than bodybuilders or other lifting styles.
The reason being is that they're constantly putting their joints and CNS under stress and they need this time off to let those recover.
If your CNS or joints start to feel sore/in knots then it's time for you to do a deload week.
I recommend about every other month, but depending on the person you may extend that out a little longer.