Coins are made in a specific size, shape, and weight so that they can be easily recognized and used as money. This is called a "coin standard." Think of it like a recipe for making a cake. Just as a cake recipe tells you exactly how much flour, sugar, and eggs to use, a coin standard tells you how much metal to use and what it should look like.
Different countries have different coin standards. For example, the United States uses a coin standard called "The United States Mint's Coin Specifications." This standard tells how much metal should be used for each coin, what the coin should look like, and how heavy it should be.
The reason for having a coin standard is so that everyone can agree on what each coin is worth. If every country had a different standard, it would be very confusing and difficult to trade goods and services between countries.
So, a coin standard is like a recipe for making coins so that they all look the same and are worth the same amount of money.