A hundred, written as 100, is a natural number that follows 99 and precedes 101. 100 is the square of 10 and can be represented as 102 or 1 × 102, or maybe most simply, 10 × 10. It is a number that is used in many different forms, and something you will likely come across all the time in your everday lives be it with math, grades, money, etc. It is also a number that can be relatively easy to work with mathematically (along with many multiples of 10), so it is frequently used in examples.
If we were to count all of the squares in the figure above, we would see that there are 100 total squares.
The number one hundred is used in many different contexts. One way it is used is in terms of scales (such as Fahrenheit and Celsius temperature scales) and percentages. 100% for example, is usually considered the maximum amount of something you can have. For example, if a box of ice cream came with 8 ice cream cones, and you had 8, you would have 100% of the ice cream in the box.
A standard American football field also measures 100 yards between the goal lines.
There are numerous other examples of the number 100 that you will come across, so it may be useful to be comfortable working with the number and its many different representations.