Indices : Terminology/Characters : En Dash

A horizontal line character one en in width—-half of an em space. Commonly use to imply duration of time, and for creating compound adjectives.

Used to indicate a closed range or a connection between two things of almost any kind. Most commonly used in date ranges.

Unicode : 2013
Windows US Keyboard : Alt 0150
Macintosh US Keyboard : Option -

Indices : Terminology/Characters : Em Dash

A horizontal line character one em in width. Commonly use to imply a break in thought, or missing content.

Used to indicate a sudden break in thought, or to show an open range such as in numbers or dates.

Unicode : 2014
Windows US Keyboard : Alt 0151
Macintosh US Keyboard : Shift Option -

Discussion:
Em Dash Usage in Broken Sentence
Space around Em Dashes?
The Em
Line Breaks and Em Dashes
How to Determine the Width of Dashes (em/en)