A "three-digit" number is any number that consists of three numerical digits, ranging from 100 to 999. Each digit can be any number from 0 to 9, but the first digit cannot be zero. For example, 123, 456, and 789 are all three-digit numbers. Three-digit numbers are commonly used in various contexts, such as in mathematics, statistics, and everyday life, like in zip codes or phone numbers. They can represent quantities, measurements, or identifiers, making them essential for organization and communication in many fields.