Zero-Width Space (U+200B) is an invisible character with zero display width. Nothing appears on screen, but it exists in text data and functions as a hint for permissible line break positions.

In languages like Thai and Khmer that do not use spaces between words, zero-width spaces serve to indicate word boundaries. Web browsers allow line breaks at these positions. Unicode explained books cover invisible character mechanics.

From a security perspective, zero-width spaces can be exploited for fingerprinting (embedding invisible identifiers in text). They can also be inadvertently introduced through copy-paste operations.

For character counting, zero-width spaces count as one character despite being invisible, causing discrepancies between visible and actual character counts. Character encoding fundamentals books provide additional context.