Dash facts for kids
The dash is a punctuation mark that is similar in appearance to the hyphen and minus sign but differs from these symbols in length and, in some fonts, height above the baseline. The most common versions of the dash are the en dash (–), longer than a hyphen; the em dash (—), longer than the en dash; and the horizontal bar (―), whose length varies across typefaces but tends to be between those of the en and em dashes.
Historically, the names of en dash and em dash came from the width of a lower-case n and upper-case M, respectively, in commonly used monospaced fonts.
Dash Facts for Kids. Kiddle Encyclopedia.