Exponential notation, sometimes called scientific notation, is an easier way of writing large numbers for use in calculations, or simply as reference points (such as astronomical or microscopic distances).
Imagine you had an equation to perform, and one part of that calculation was 8 x 8 x 8 x 8 x 8 x 8 x 8. Say also you had to use that calculation several times over - it would soon get pretty tiresome, and use up unnecessary space. Therefore, we use 8 to the power of 7 or 87.
An astronomer wanting to note down the distance to the Andromeda galaxy would run out of ink if he had to write the number out in full. Much better to write 2.4×1019 km than the sum of 2.4 million times the speed of light!
Any number can be written as exponential notation.
For example, the number 1 can be written as 1 x 100.
To give another instance, 4,510,000, 000 can be given as 4.51 x 109
If you'd like to read other Blurtit answers on the subject of exponential notation, check out What is a exponential notation? And how can you find it? or How Do I Write 3125 In Exponential Notation?
This film explains more on working out exponents: