Decimal comes from the Latin word decimus, meaning tenth, from the root word decem, or 10. The decimal system, therefore, has 10 as its base and is sometimes called a base-10 system. Decimal can also specifically refer to a number in the decimal system. As an adjective, decimal means something related to this numbering system. The decimal point, for example, refers to the period that separates the ones place from the tenths place in decimal numbers.
Decimals are another way of representing fractions or a part of a whole. Before the decimal point(.), there is the whole number(4.) and after it is the part selected(4.6). It can also be used for proper fractions(0.6). Each place after the decimal point, the numbers' values are decreasing, but on the other hand before the decimal the values are increasing. For example, 40.46576767888. The numbers after the decimal, if they were before the decimal, they would have been huge numbers. But in case of decimals, it's just the opposite.