Typically, fasting is going without food for a period of time. The length of time could be for one meal up to several days. But don’t attempt a prolonged fast without first receiving instruction on how to appropriately do so.
Sometimes people will fast from certain foods or categories of food. Other types of fasts are more general, such as abstaining from a certain activity or pursuit.
The important thing in any fast is to do it for the right reasons. Fasting for the wrong purpose will accomplish little. Isaiah talked about fasting with the proper attitude and motives (Isaiah 58:3-14).