Three-digit numbers are numerical values that range from 100 to 999. They consist of three places: the hundreds, the tens, and the units. For example, in the number 345, the digit 3 represents the hundreds place, 4 represents the tens place, and 5 represents the units place. Each digit in a three-digit number contributes to its overall value. The hundreds place has the highest value, followed by the tens and then the units. This structure allows for a wide variety of combinations, making three-digit numbers essential in everyday counting, measuring, and organizing information.