Divot
A divot is the piece of turf your club lifts out of the ground.
A divot forms on iron shots from the fairway: the clubface dives into the ground after the ball and lifts out a patch of turf. Clean contact with a divot is even considered a sign of a correctly struck ball, because the club hits the ball before the ground. On the driving range with mats no divot forms, which is why range and course feel different. The lifted-out turf is also called a divot.
Etiquette demands the handling afterwards: either you place the piece back into the scar and press it down, or you fill the spot with a sand-seed mixture. Which of the two applies depends on the course and is often posted at the cart or in the club office. An example: on a par 4 you hit your 7 iron from the fairway. The scar is clean, the piece lies three metres ahead. You fetch it, place it in and tread it down. That way the spot heals in days instead of weeks.
One misunderstanding concerns the rulebook: if your ball lies in an old divot scar, there is normally no relief. The scar counts as part of the course, you play the ball as it lies. Exceptions are governed by the local rules, for example freshly seeded spots as "ground under repair". If in doubt the notice board or the FAQs on the topic of local rules will help.
FAQ
Do I have to replace the divot or fill it with sand?
That depends on the course, and the instruction is usually posted at the cart, on the tee or in the club office. Replacing and treading down is the classic variant; the sand-seed mixture is preferred on many well-maintained facilities because it grows back faster and more evenly. If you are unsure, look at what the players in front of you do — and if in doubt, sand is the safer choice.
May I prefer my ball if it lies in an old divot scar?
Normally no — the scar counts as part of the course, you play the ball as it lies. There is only an exception if the spot is designated as ground under repair by the local rule, for example freshly seeded scars. If nothing is posted on the notice board or the scorecard, the rule is: no relief, even if it feels unfair.
Is a divot on an iron shot a good sign?
Yes, a clean, flat divot after the ball shows that you hit the ball before the ground — that is exactly how the iron shot should work. A huge, deep piece of turf, on the other hand, points to a swing that is too steep, and no turf contact at all can indicate picking the ball. On the driving range with mats this feedback is missing, which is why the course feels different from practice.