Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. It doesn't specify which foods you should eat but rather when you should eat them. In this respect, it's not a diet in the conventional sense but more accurately described as an eating pattern.
Intermittent fasting has recently received a lot of attention as a way to lose weight. With intermittent fasting, people restrict themselves to eating during a certain time frame. For instance, someone might eat during an 8-hour window from noon to 8 pm, so they would be fasting for 16 hours. Alternatively, someone might fast for 24 hours once a week. There are several other variations of intermittent fasting, all of which can help someone lose weight. When people consume food, their insulin goes up. Their body processes the food, turning it into glucose, which fuels the body. Any excess sugar gets stored as fat for later use. When someone fasts for 10 to 12 hours, the body is able to use up the stored glucose.  Once the glucose stores are used up, the body switches to the sugars stored in fat as a fuel source. When fasting, the body continues to burn calories, but instead of coming from food, they are coming from fat stores, allowing you to lose weight. 
Rejecting the premises