Digit/ˈdɪdʒɪt/ Definition 1 of 3Pro Tip 1/3Math Operations Used in arithmetic to perform calculations like addition and subtraction. Calculate the sum of these digits: 8 + 4. Pro Tip 2/3Phone Numbers Commonly required to complete forms and when sharing contact info. My phone number has ten digits. Pro Tip 3/3PIN Codes Consist of digits and keep personal information like bank accounts secure. Your bank PIN is a four-digit code.