###### Definition6.1.22

A positive number is written in scientific notation when it has the form $$a \times 10^n$$ where $$n$$ is an integer and $$1 \le a \lt 10 \text{.}$$ In other words, $$a$$ has precisely one digit to the left of the decimal place. The exponent $$n$$ used here is called the number's order of magnitude. The number $$a$$ is sometimes called the significand or the mantissa.

in-context