What is a cheat day?

In one line

A cheat day is a day during a diet when you set your planned meals aside and eat the foods you want, without a set amount.

What is a cheat day?
A table full of food among diet photos
On the social media of someone watching their diet, a photo full of high-calorie food suddenly appears. The caption says 'today is my cheat day.' So what kind of day is a cheat day, exactly?
In one line
A day to set the diet aside and eat what you want
A cheat day is a day during a period of controlled eating when you do not follow your planned meals and eat the foods you want. How much and what to eat are not decided ahead of time. After that day, you go back to your usual diet.
What the word means
'Cheat' means acting dishonestly
The English word 'cheat' means to act dishonestly to get what you want, as in cheating on a test or breaking the rules in a game. 'Cheat day' is used to mean a day when you step outside your own diet rules on purpose.
Cheat meal and cheat day
One meal or a whole day
Eating off-plan food for one meal is called a 'cheat meal'; stretching it to a whole day is a 'cheat day'. Some people spread it over several days, such as a weekend. In every case, the amount is not set ahead of time.
How it differs from a refeed
There is no target amount
A 'refeed' sets a plan to eat more, mostly carbohydrates, up to about the calories that keep your weight the same ('maintenance calories'). A cheat day has no such target amount or target nutrient. Both are days of eating more during a diet, but the difference is whether there is a planned amount.
What is eaten?
Very large amounts of high-calorie food
A study that analyzed cheat meal photos found that most showed high-calorie foods, and more than half showed very large amounts. In a survey of young people, the most common answer for the amount eaten at one time was 1,000-1,499 kcal.
Why do it?
To ease cravings and stick with the diet
People who planned their cheat meals said they did it to ease cravings and to keep following a strict diet. A mental rest, a short pause from a diet you have been holding to for a long time, is also named as a reason.
A point of caution
Binge-like eating showed up alongside it
'Binge eating' means eating far too much at once and finding it hard to stop even when full. In a survey of young people, eating problems such as binge eating showed up more often among those who had cheat meals. Nutrition advice for people preparing for bodybuilding contests advises against cheat days without a set amount in many cases.
Common myth / Is all the weight gained the next day fat?
It includes water stored with glycogen
Carbohydrates eaten in large amounts are stored in the liver and muscles as 'glycogen', and each 1 g of glycogen holds 3 g or more of water. So even if your weight jumps the day after a cheat day, not all of that weight is fat. When the body uses the glycogen again, this water leaves too.
Summary
A day of eating what you want without a set amount
A cheat day is a day during a diet when you set your planned meals aside and eat the foods you want. The weight gained the next day includes water stored with glycogen, so not all of it is added fat. Related terms: cheat meal, refeed, glycogen, binge eating.