This is a hyphen: – (a dash, which is longer, looks like this: —).
The hyphen is a small punctuation mark that can, nonetheless, prevent much misunderstanding. Egregious Examples follow:
Let’s say you’re writing a story about a 20-year-old who loves old films. You pen, “Bill Jones is an old film buff.” But didn’t I say he was 20? How can he be an old film buff?
Much better: “Bill Jones is an old-film buff.”
If you write, “I’m a small business owner,” my question would be thus: How small are you?
Inserting a hyphen — “I’m a small-business owner” — makes all the difference.
You can even avoid being sued if you use hyphens correctly! Let’s assume that you’re a newspaper reporter, and you interview a man who is a vocal supporter of gay rights. You file your story about him and, in it, write, “Bill Jones is a gay rights activist.” His attorney calls your editor at the newspaper: “Bill Jones isn’t a ‘rights activist’ who is gay! He has a wife and seven children! We’re suing your paper for libel and want $10 million for damage to his reputation!”
To avoid this, you should have used that tiny little hyphen: “Bill Jones is a gay-rights activist.”