Reversible numbers are numbers that remain the same when their digits are reversed. For example, the number 123 becomes 321 when reversed, but it is not a reversible number because the two values are different. A true reversible number, like 121, reads the same forwards and backwards. These numbers are often discussed in the context of palindromes, which are sequences that exhibit this symmetry. Reversible numbers can be found in various numerical systems and are sometimes used in puzzles and games to challenge mathematical thinking.