Definition 6.2.4

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.

Some conventions do not require \(a\) to be between \(1\) and \(10\text{,}\) excluding both values, but that is the convention used in this book.

in-context