It is true that the number 1.255 is an example of a decimal number.
A decimal number refers to numerical representation that uses the base-10 system where each digit can have one of ten possible values (0 through 9). In the number 1.255, the decimal point separates the whole number part (1) from the fractional part (0.255).
So, the presence of the decimal point is a defining characteristic of decimal numbers as it indicates the division between the whole and fractional portions.
This allows for the representation of numbers that are not whole such as fractions (i.e. 1/4) making 1.255 a clear example of a decimal number in the base-10 numbering system.