What is a decimal number?

A decimal number is defined as a number that includes a decimal point, which signifies that it has a whole part and a fractional part, where the fractional part represents a value less than one. This system allows for the representation of values that lie between whole numbers. For example, in the number 3.14, "3" is the whole part, while ".14" indicates the fractional part, showing that it is not a whole number but represents a quantity that is less than four.

In contrast, the other options describe different concepts: using only whole numbers pertains to integers, while a number divisible by 10 does not necessarily indicate a decimal. Lastly, the notion of using digits 0 through 9 refers to the numeral system rather than the specific nature of decimal numbers. Therefore, the option that identifies a decimal number as one with a decimal point showing a part less than one is the most accurate.