Empty string
the unique string of length zero
In formal language theory, the empty string, also known as the empty word or null string, is the unique string of length zero.
Formal theory
Formally, a string is a finite, ordered sequence of characters such as letters, digits or spaces. The empty string is the special case where the sequence has length zero, so there are no symbols in the string.
There is only one empty string, because two strings are only different if they have different lengths or a different sequence of symbols.
In formal treatments, the empty string is denoted with ε or sometimes Λ or λ.
The empty string should not be confused with the empty language ∅, which is a formal language (i.e. a set of strings) that contains no strings, not even the empty string.
The empty string has several properties:
|ε| = 0. Its string length is zero.
ε ⋅ s = s ⋅ ε = s.
The public source identifies “Empty string” as the unique string of length zero. This brief keeps that definition visible, then builds a research path around Empty, string and unique.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Apr 21, 2026. The linked authority identifier is Q670834. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Empty string” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.