Quick and simple question!

On my website I have my permalink set to "randomwebsite / sample-post"

What does the dash stand for in the URL? Does it stand for a space for the search engines?

I have a website and I'm wondering if I should make my "randomwebsite/facebookreview" or "randomwebsite/facebook-review"

Which one is going to rank better? Sorry, I can't post links yet. This looks kind of ghetto. I hope you understand what I'm asking.
Please explain..

Good day, i understand your concern.Well in SEO it really does not matter , as Google Head of Web Spam Team , Matt cutt suggested that having a (-)(_) does not make a difference in ranking high.