When you cook something, like a big pot of soup, it gets very hot. If you want to keep it hot and fresh for a long time, you need to make sure the temperature stays high enough to keep all the germs away. That's where recovery time comes in.
Recovery time is the amount of time it takes for a big pot of hot soup (or any other food) to get back up to the right temperature after you take some out to serve. When you take soup out of the pot, you're also taking some of the heat away. The longer the pot sits there without heating up again, the more germs can grow in the soup.
So, to make sure your soup stays healthy for everyone to eat, you need to let it recover. That means put some more heat into the pot and let it warm back up. It usually takes about 20-30 minutes for a pot to fully recover after you take some out. This way, you can keep adding more food to the pot throughout the day and know it's always safe to eat.