Zero-width space
The zero-width space , abbreviated ZWSP, is a non-printing character used in computerized typesetting to indicate word boundaries to text-processing systems for scripts that do not use explicit spacing, or after characters not followed by a visible space after which there may be a line break. Purpose 
The zero-width space marks a potential line break without hyphenation; for hyphenated line breaks, a soft hyphen is used. The zero-width space can be used to mark word breaks in languages without visible space between words, such as Thai, Myanmar, Khmer, and Japanese. Unlike fixed-width spaces, in justified text that increases spacing between letters, characters adjacent to the zero-width space are spaced as if it was not present. Example
To show the effect of the zero-width space, the following words have been separated with zero-width spaces:

And the following words are not separated with these spaces:

On browsers supporting zero-width spaces, resizing the window will re-break the first text only at word boundaries, while the second text will not be broken at all. Usage

HTML
In HTML pages, the HTML element <wbr> functions as a zero-width space. In Internet Explorer 6, the zero-width space was not supported in some fonts. Prohibition in domain names
ICANN rules prohibit domain names from containing non-displayed characters, including the zero-width space, and most browsers prohibit their use within domain names because they can be used to create a homograph attack, where a malicious URL is visually indistinguishable from a legitimate one. Encoding 
The zero-width space character is encoded in Unicode as , and input in HTML as ,  or . Contrary to what their names suggest, the character entities &NegativeThickSpace;, &NegativeMediumSpace;, &NegativeThinSpace;, and &NegativeVeryThinSpace; also refer to the zero-width space. The TeX representation is ; the LaTeX representation is \hspace{0pt}; and the groff representation is \:. Its semantics and HTML implementation are similar to the soft hyphen, except that soft hyphens display a hyphen character at the point where the line is broken. See also 
 Hair space
 Whitespace character – including a table comparing various space-like characters
 Word divider
 Word wrapping
 Word joiner (U+2060: ⁠), as well as zero-width no-break space (U+FEFF: )
 Zero-width joiner (U+200D: ‍)
 Zero-width non-joiner (U+200C: ‌)

References

Citations

Sources 

 

Control characters
Typography
Unicode formatting code points
Whitespace