Intermittent fasting (IF) is a term for an eating pattern that cycles between periods of fasting and eating.
It does not say anything about which foods you should eat, but rather when you should eat them.
In this respect, it is not a "diet" in the conventional sense. It is more accurately described as an "eating pattern."
Common intermittent fasting methods involve daily 16 hour fasts, or fasting for 24 hours, twice per week.