0 may refer to:

• 0 (number), the integer between -1 and +1
• 0 (year), a year used in some calendar systems
• Slashed zero, a glyph used to distinguish the numeral 0 from the letter O
• 0 or #0, stage name of American musician Sid Wilson, when performing with the band Slipknot
• #0, a Spanish TV channel formerly known as Canal+

0 (zero; BrE: or AmE: ) is both a number and the numerical digit used to represent that number in numerals. It fulfills a central role in mathematics as the additive identity of the integers, real numbers, and many other algebraic structures. As a digit, 0 is used as a placeholder in place value systems. Names for the number 0 in English include zero, nought or (US) naught , nil, or — in contexts where at least one adjacent digit distinguishes it from the letter "O" — oh or o . Informal or slang terms for zero include zilch and zip. Ought and aught , as well as cipher, have also been used historically.

In mathematics, division by zero is division where the divisor (denominator) is zero. Such a division can be formally expressed as a/0 where a is the dividend (numerator). In ordinary arithmetic, the expression has no meaning, as there is no number which, multiplied by 0, gives a (assuming a≠0), and so division by zero is undefined. Since any number multiplied by zero is zero, the expression 0/0 also has no defined value; when it is the form of a limit, it is an indeterminate form. Historically, one of the earliest recorded references to the mathematical impossibility of assigning a value to a/0 is contained in George Berkeley's criticism of infinitesimal calculus in The Analyst ("ghosts of departed quantities").

An emoticon ( or ), etymologically a portmanteau of emotion and icon, is a metacommunicative pictorial representation of a facial expression that, in the absence of body language and prosody, serves to draw a receiver's attention to the tenor or temper of a sender's nominal non-verbal communication, changing and improving its interpretation. It expresses — usually by means of punctuation marks (though it can include numbers and letters) — a person's feelings or mood, though as emoticons have become more popular, some devices have provided stylized pictures that do not use punctuation.

The null character (also null terminator), abbreviated NUL, is a control character with the value zero. It is present in many character sets, including ISO/IEC 646 (or ASCII), the C0 control code, the Universal Character Set (or Unicode), and EBCDIC. It is available in nearly all mainstream programming languages.

Signed zero is zero with an associated sign. In ordinary arithmetic, the number 0 does not have a sign, so that -0, +0 and 0 are identical. However, in  computing, some number representations allow for the existence of two zeros, often denoted by -0 (negative zero) and +0 (positive zero), regarded as equal by the numerical comparison operations but with possible different behaviors in particular operations. This occurs in the sign and magnitude and ones' complement signed number representations for integers, and in most floating-point number representations. The number 0 is usually encoded as +0, but can be represented by either +0 or -0.

Theta (uppercase Θ or ϴ, lowercase θ (which resembles digit 0 with horizontal line) or ϑ; , thē̂ta, ; Modern: , thī́ta, ; , ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth . In the system of Greek numerals it has a value of 9.

Unicode has subscripted and superscripted versions of a number of characters including a full set of arabic numerals. These characters allow any polynomial,  chemical and certain other equations to be represented in plain text without using any form of markup like HTML or TeX.