Also found in: Wikipedia.
Related to emdash: endash
em·dashor em dash (ĕm′dăsh′)
A symbol ( — ) used in writing and printing to indicate a break in thought or sentence structure, to introduce a phrase added for emphasis, definition, or explanation, or to separate two clauses.
[From its being the width of an m in printing.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.