Nailing the crucial difference between these types of punctuation can nudge experienced readers in your favor—something that is incredibly important during the college application process. The hyphen, en dash, and em dash are distinguished by, at most, a few pixels on your screen and their uses are similarly nuanced.
Used to join intimately linked compound terms, the hyphen clarifies the relation among different words.
Example: “Long-term exposure to tobacco smoke can increase your risk of cancer”
The words “long” and “term” are meant to jointly describe the word “exposure”.
Other Examples: high-risk, free-for-all, eye-opener, all-American
The En Dash
The en dash is slightly longer than the hyphen and it is meant to denote items related by distance or time1.
Example: We are looking for students ages 13–20.
This can also be applied to date ranges and prefixes fixed to proper nouns if they denote a temporal relationship.
Other Examples: April–June, pre–Revolutionary War, 30–50 feet long
The Em Dash
The em dash is the longest of these punctuation marks and is also the most versatile. It works like parentheses to add a thought or an extra piece to the sentence. The use of the em dash is more subjective and is meant to enhance the reader’s experience than to denote a relationship between two words.
Example: I went to the concert—something I thought was a great idea until it rained.
The em dash can replace parentheses, colons, and commas, depending on how you’d like to use them. Keep in mind you shouldn’t be using more than two em dashes in a sentence
Other Example: My brother—the one who originally hated the idea—was totally on board this time around.
Check out these great resources for more details on proper punctuation: