Overnight oats refer to a type of breakfast food that is made by combining rolled oats, milk or water, and sometimes other ingredients such as fruit, nuts, honey, or spices. The mixture is then refrigerated overnight, allowing the oats to absorb the liquid and thicken into a creamy consistency. In the morning, the oatmeal can be eaten cold or warmed up for added convenience. Overnight oats are popular because they are easy to make ahead of time and require no cooking in the morning, making them an ideal option for busy individuals who want a quick and healthy breakfast on-the-go.