the number that is represented as a one followed by 12 zeros; in the United Kingdom the usage followed in the United States is frequently seen
"The company recently announced it had raised five billion dollars, reflecting the modern convention of writing this figure as 10 to the twelfth power."
the number that is represented as a one followed by 9 zeros
"The company's latest financial report revealed annual revenue exceeding five billion dollars, marking a historic milestone for its shareholders."
a thousand million (1,000 × 1,000^2): 1 followed by nine zeros, 10⁹; a milliard
"The company announced that its new data center would cost two billion dollars to build."
In plain English: A billion is a number equal to one thousand million, which is a huge amount of money or things.
"The new stadium project will cost five billion dollars to complete."
Usage: Use "billion" to mean one thousand million, which equals one followed by nine zeros. This short form is standard in modern English for that specific large quantity.
denoting a quantity consisting of one thousand million items or units in the United States
"The new tech company reported earning two billion dollars in revenue last year, which is a massive sum by American standards."
denoting a quantity consisting of one million million items or units in Great Britain
"When the British prime minister announced the new infrastructure budget, he stated it would cost half a billion pounds to build the high-speed rail line."
The word entered English from French, where it originally combined the prefix meaning "two" with a suffix for large numbers to denote two million. Over time, its value shifted dramatically in English usage to represent a much larger figure than its French counterpart.