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A hyphen is a punctuation mark. It is used both to join words and to separate syllables. It is often confused with a dash, which is longer. Hyphenation is the use of hyphens.

In computer programming notation, the hyphen corresponds to Unicode and ASCII character 45, or 0x002D (see hexadecimal).

Rules and customs of usage

Traditionally, the hypen has been used in several ways:

However, the use of hyphens has in general been steadily declining, both in popular writing and in scholarly journals. Its use is almost always avoided by those who write advertising copy or labels on packaging, since they are often more concerned with visual cleanliness than semantic clarity. However, it is still used in most newspapers and magazines, so people remain accustomed to seeing and understanding it. Most writers who are obstreperous about other things are compliant when editors tell them to hyphenate compounds.

Examples of usage

Some strong examples of semantic changes caused by the placement of hyphens:

Additional examples of proper use:
text-only document (but ... document is text only)
Detroit-based organization (but ... organization is Detroit based)
state-of-the-art product (but ... product is state of the art)
board-certified strategy (but ... strategy is board certified)
thought-provoking argument (but ... argument is thought provoking)
time-sensitive error (but ... error is time sensitive)
case-sensitive password (but ... password is case sensitive)
government-issued photo ID (but ... photo ID is government issued, or, better, ... is issued by the government)
light-gathering surface (but ... surface is light gathering)
award-winning novel (but ... novel is award winning, or, more likely, ... won an award)
web-based encyclopedia (but ... encyclopedia is web based)
fun-loving person (but ... person is fun loving)
how to wire-transfer funds
how to tax-plan
advertising-supported service (but ... service is advertising supported, or, better, ... is supported by advertising)
Rudolph Giuliani is an Italian-American (but see Hyphenated American)
list of China-related topics (but ... list of topics is China related, or, better, ... related to China)
Out-of-body experience
Near-death experience