Dash

The dash is a punctuation mark that is usually written in the middle of a line of text. A hyphen is sometimes called a dash, but it is used differently.

Dashes are used to add more drama to writing. The two main forms of dashes are:
 The en dash (–) is the shorter of the two. It is longer than a hyphen but shorter than an em dash. In normal text it is about the width of the letter "n". An en dash is used to connect two numbers that make up a range (for example pages 3–6). It is also used to show a range of dates (2010–2011) or of time (11:30 a.m.–1:30 p.m.). 
 The em dash (—) is so-named because it is about the length of an uppercase M. They are best used to show emphasis or for an interruption in thought. They can also be used in place of a comma, parentheses, or a colon. But they are less formal than the punctuation marks they replace.

 References 

 Other websites 
 English Grammar Basics: How to Use a Dash; YouTube

Category:Punctuation