The phrase "quick boil" means to rapidly heat a liquid until it starts boiling, which happens when it reaches a high temperature and starts bubbling. Full definition
Bring to quick boil then simmer for about 10 minutes until most of water has evaporated from pan and onions are soft. (heyketomama.com)
For example, we've seen evidence suggesting a moderate loss of pantothenic acid with quick boiled spinach. (whfoods.org)
Beet greens are only one of three vegetables we recommend Quick Boiling to free up acids and allow them to leach into the boiling water; this brings out a sweeter taste from the beet greens. (whfoods.org)