What is o in roman numerals?

Answer 1

There is only one known instance where there was a glyph (linguistic symbol, such as a letter) for "0". It was the letter N, for the latin "nulla", meaning none. It was written by Saint Bede in the year 725, and called "nullae". Roman Numerals:

Symbol Value Name

N 0 (zero) (nullae) *

I 1 (one) (unus)

V 5 (five) (quinque)

X 10 (ten) (decem)

L 50 (fifty) (quinquaginta)

C 100 (one hundred) (centum)

D 500 (five hundred) (quingenti)

M 1000 (one thousand) (mille)

* Non-standard Roman numeral used by St. Bede.

Source: http://roman.sourceforge.net/

Answer 2

There is no O in the Roman numeral system. The chief defect of the system is the lack of zero, or naught, or any way of showing nothing.