0O

0O is a two-character sequence consisting of the digit zero (0) followed by the capital letter O. It does not denote a single standardized concept on its own, but it appears in various contexts where zero and the letter O are juxtaposed, often leading to confusion with similar-looking characters or with other numeric prefixes such as 0o.

In typography, the close visual similarity between 0 and O can cause misreadings in code, identifiers, and data. To reduce ambiguity, many fonts offer a slashed or dotted zero, and some programming environments enforce distinct styling for numerals and letters in identifiers. Context often clarifies meaning, but readers may still confuse 0O with 0 and O or with the lowercase o.

In programming and computer science, a closely related use of 0O arises as a potential prefix for octal numbers. In several languages, the prefix 0o or 0O denotes octal (base 8) literals, followed by octal digits. For example, in languages that allow it, 0o77 or 0O77 represents the decimal number 63. The exact syntax is language-dependent, and many languages are case-sensitive regarding the O; some accept both 0o and 0O, while others restrict to a lowercase o. Outside of octal notation, 0O does not carry a standard universal meaning.

Other uses of the sequence are typically accidental or contextual, such as part of product codes, filenames, or identifiers where neither the zero nor the letter O carries intrinsic mathematical or linguistic meaning.

See also: zero, letter O, octal notation, numeric prefixes, typographic confusion.