1. The problem is to understand what a decimal number is. 2. A decimal number is a number that uses a decimal point to separate the whole part from the fractional part. 3. For example, in the number $12.34$, $12$ is the whole part and $34$ is the fractional part. 4. Decimal numbers can represent fractions and are used in everyday counting and measurements. 5. The decimal system is base 10, meaning each digit represents a power of 10 depending on its position relative to the decimal point. 6. For instance, $12.34 = 1 \times 10^1 + 2 \times 10^0 + 3 \times 10^{-1} + 4 \times 10^{-2}$. 7. Understanding decimal numbers is fundamental in algebra, arithmetic, and many areas of science and engineering.