View more at http://www.MathAndScience.com. In this lesson, we will learn what a percentage is and understand why percent is an important concept in math. A percent is when we express something as it compares to the number 100. The word percent literally means "per one hundred". We use percent when discussing probability, fractions, statistics, interest rates, and numerous other subjects. Here we learn how to express a given percent in terms of a fraction and a decimal so that when we solve percent problems, we will know how to carry out the operations.