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Em dash code-point: U+2014 (html: —)

An em dash, or em-dash, is a dash the width of an M in the font and point size it is printed in (hence the name 'em').

An em dash is used:

• to suround a parenthetical statement where more emphasis is needed than would be provided by parenthasise.
• in place of a semicolon to link related clauses in a single sentence.
• to indicate an open number range such as a date range where the beginning or ending year is not known (e.g., 1959— )
  

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En dash code-point: U+2013 (html: –)

An en dash or en-dash is the width of an 'N' in the font and point size it is printed in (hence the name 'en'). It is half the width of an em dash.