When you count things, sometimes you use your fingers or sometimes you use numbers like 1, 2, 3, and so on. When you use numbers, you count up to a certain number before you start over. For example, when you count to 9, you start over again from 1 and have to add another number to the left like 10. This way of counting is called a base-10 system.
Decimalisation is when people changed how they counted money from using 1 penny, 2 pennies, 3 pennies, to a new way of counting that makes it easier to work with larger numbers. They changed it so that instead of counting by twos and ones, we now count by tens and hundreds.
This new way of counting is called decimalisation. It means that instead of using fractions, we use decimal points to show how much money we have. This also makes it easier to calculate how much change we should get back when we buy something. We can also compare prices much more easily. For example, if one thing costs $0.50 and another costs $0.25, we know instantly which is cheaper by looking at the numbers after the decimal point.
Decimalisation also made it easier for businesses to do their accounts because they didn't have to worry about calculating using fractions. Overall, decimalisation was a way of making counting and calculating money simpler and more efficient.