Dividend CAGR is the average yearly growth rate of the per-share dividend over a stretch of time (5 years by default here). A business growing its dividend at 8% a year doubles the owner's income roughly every nine years.
Dividend growth kept up for decades is the mark of a true compounder. Coca-Cola, Procter & Gamble, and similar businesses are prized for it. But watch out for dividend growth that comes from paying out a bigger and bigger share of earnings, because that eventually hits a wall. Healthy dividend growth comes from growing earnings, not from handing out a larger slice of the same profit.