A nonalphanumeric character is a character, or symbol, that appears on a keyboard that is not a number or a letter, including punctuation and mathematical symbols. Some password conventions require users to select at least one nonalphanumeric character to be part of their passwords for heightened security.
Sometimes referred to as nonalpha characters, nonalphanumeric characters include punctuation marks, such as commas, periods, exclamation points, quote marks, colons, question marks and semicolons. Other nonalphanumeric characters that commonly appear on keyboards include dollar signs, ampersands, asterisks, plus signs, equals signs, underscores, tildes, percent symbols and slashes. Any symbol on a keyboard that is not a part of the 26-letter alphabet or a numeric character (typically 1-0), can be considered a nonalphanumeric character.