The number "999,999,999" is a nine-digit integer that is one less than one billion. It is often used in mathematics and finance to represent a large quantity just below a significant milestone. In the decimal system, it is the highest number that can be formed with nine digits. In terms of place value, "999,999,999" consists of nine nines, each representing a different place: units, tens, hundreds, thousands, ten thousands, hundred thousands, millions, ten millions, and hundred millions. This number is significant in various contexts, such as counting, statistics, and data representation in fields like computer science and economics.