An em dash (-) is a punctuation mark that is roughly the width of the capital letter "M" in a given typeface, which is why it is called an "em" dash

. It is longer than both the hyphen (-) and the en dash (–)

Uses of the Em Dash

• It creates a strong break or interruption in the structure of a sentence, often adding emphasis or drawing attention to additional information

• It can replace commas, parentheses, colons, or semicolons to set off parenthetical or explanatory elements in a sentence, often making the sentence more striking or dramatic

• It can indicate a sudden change in thought or direction within a sentence

• It can be used to introduce a summary or amplification after a list or series of phrases

• It can substitute for quotation marks or add suspense in writing

• It is often used without spaces on either side, though some style guides allow spaces

Examples

• Setting off parenthetical information:
  Jimi Hendrix- a master guitar player if there ever was one-was left-handed.

• Indicating a sudden change:
  Most experts thought it would be a rebuilding year for the team, but Coach Clippard-she knew otherwise.

• Introducing a summary:
  Village Wok, the Big 10, the iconic two-story McDonald’s-the list kept growing.

In summary, the em dash is a versatile punctuation mark used to create emphasis, indicate breaks in thought, and replace other punctuation marks for stylistic effect