Percentage used in mathematics to give you a number that describes the value that the given percentage is less than that.
Example: Let's say we have an array of the ages of all the people that lives in a street.
ages = [5,31,43,48,50,41,7,11,15,39,80,82,32,2,8,6,25,36,27,61,31]
In a computer sense, a data set is any data collection. It can be anything from a program to a complete website.