ENUM and SET are similar datatypes which is used to make a predefined choices to select value(s) among them to be stored on the database
Example
ENUM('Male','Female') , this filed can carry the value of 'Female' or 'Male' ONLY and not any other value, so you can select one value from the predefined values "Suitable for HTML Radio Buttons"
SET is the same as ENUM but you can choose any number of values you want,
Example:
SET('Football','Basketball','Tennis','Handball'), you can any values you want and it will be stored on the database as a string of comma separated values. "Suitable for HTML Checkboxes"