A billion is a large number equal to 1,000,000,000, which is one followed by nine zeros. In terms of millions, one billion is one thousand million. There are two distinct definitions of a billion: the short-scale definition, which is commonly used in the United States, Canada, and France, and the long-scale definition, which is used in some European countries such as the United Kingdom, Australia, and many other European countries. The short-scale definition of a billion is 1,000,000,000, while the long-scale definition is 1,000,000,000,000, which is one million million. It is important to be aware of which definition of a billion is being used to avoid misunderstandings, especially in international contexts.

To help visualize how large a billion is, here are some examples:

• A stack of paper 1,000 inches (or 83 feet, four inches) tall would represent a billion years.
• The age of the Earth is 4.6 billion years, which would require a stack of paper 4,600 inches tall, or 383 feet and 4 inches.
• One billion oranges would fill a stadium to the brim.
• If you saved $100 every day, it would take you and 304 generations of your descendants to save up one billion dollars.

In summary, a billion is a very large number equal to 1,000,000,000, which is one followed by nine zeros. It is important to be aware of which definition of a billion is being used, as there are two distinct definitions.