A hard-boiled egg is a cooked egg where both the white and yolk are firm. To prepare one, an egg is typically placed in boiling water for about 9 to 12 minutes. After cooking, it is cooled in cold water to stop the cooking process and make peeling easier. Hard-boiled eggs are a popular snack and can be used in various dishes, such as salads and sandwiches. They are a good source of protein and contain essential nutrients like vitamins A, D, and B12. Many people enjoy them for their convenience and versatility in meals.