A decimal number can be defined as a number whose whole number part and the fractional part is separated by a decimal point.

Explanation: Let us discuss decimal.
A number whose decimal part and whole number part are separated by a point is called decimal.

For example, \$63.4\$.
Here, \$63\$ and \$4\$ are separated by a point. So, \$63.4\$ is a decimal number.

Subtracting decimals means finding the difference between decimal numbers.

Explanation: In this image we are subtracting two decimal numbers \$15.5\$ from \$14.3\$ we get \$1.2\$.