What is the definition of digital

What is the definition of digital

For example, the sum of 1234 + 2345 + 4567 digits is (4 + 5 + 7) (individual digits) + (3 + 4 + 6) (ten digits) + (2 + 3 + 5) (hundred digits) + (1 + 2 + 4) (thousand digits)?