An uncertain number is a quantity that is not known or cannot be determined. It can refer to a range of numbers, such as 'SOME' or 'ANY', or it can refer to an exact number that is unknown. The term 'uncertain number' is often used in mathematics and statistics to describe a situation where the exact amount is unknown. In crossword puzzles, the terms 'SOME' and 'ANY' are often used to indicate an uncertain number.