०
Tenth century “West Arabic” variation of the Nepali form of Hindu-Arabic numeral ٠(0) (compare Devanāgarī script ०), adopted for use with the Latin script in Europe as 1

The pronunciation as a digit is very often shortened to that of the letter O to save time or keep rhythm. This change is required for the tens place of minutes following the hour and in shortened pronunciation of numbers between 10 and 19 hundred, including years, as well as their truncated two-digit forms, where the zero is a leading digit. It is also very common when saying telephone numbers, decimals after the decimal point, the leading zero in decimal fractions less than one, or many other words such as 007.