Uppercase numbers, also known as capital letters, are a type of character that can be used in passwords. They are the same characters as those used in the English alphabet, but instead of being lowercase (a-z), they are uppercase (A-Z). Uppercase numbers add an extra layer of complexity to passwords since they require users to input both lowercase and uppercase characters when entering their password. By adding this additional level of complexity, it helps make passwords more secure as it makes them harder for unauthorized individuals to guess or crack.