noun

• (mathematics) A position in a sequence of numerals representing a place value in a positional number system.
  "The base-10 number 123.4 has four digits: the hundreds digit is 1, the tens digit is 2, the units digit is 3, and the tenths digit is 4."
• (mathematics) A distinct symbol representing a natural number in a positional number system.
  "Hexadecimal numeration (Base sixteen) includes the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 but also A (=10 decimal), B, C, D, E, and F. Sixteen itself is written as the two-digit number 10."
• (units of measure, astronomy) ¹⁄₁₂ the apparent diameter of the sun or moon, (chiefly) as a measure of the totality of an eclipse.
  "A six-digit eclipse covers half the lunar surface."
• (historical units of measure) A unit of length notionally based upon the width of an adult human finger, standardized differently in various places and times, (especially) the English digit of ¹⁄₁₆ foot, now equivalent to about 1.9 cm.

verb

• (archaic, transitive) To point at or point out with the finger.