Dashes, specifically em dashes, represent abrupt pauses or breaks in thought or surround parenthetical elements that use commas. These are the universally accepted uses of the dash—
A dash represents a pause or break in thought.
Dashes surround parenthetical elements that use commas.
Note: The AP Stylebook and The New York Times Manual of Style and Usage specify that spaces surround a dash for typographical purposes.
Note: For dashes used for ranges and occasional word linkages, see en dashes.
Note: The Chicago Manual of Style and The New York Times Manual of Style and Usage recommend using no more than two dashes in a sentence.