URLs: Dash vs. Underscores
Consider using punctuation in your URLs. The URL http://www.example.com/green-dress.html is much more useful to us than http://www.example.com/greendress.html. We recommend that you use hyphens (-) instead of underscores (_) in your URLs.
Dashes are recommended by Google over underscores.
Dashes are more familiar to the end user.
Dashes are easier to write on a standard keyboard (no need to Shift).
Dashes don’t hide behind underlines.
Dashes feel more native in the context of URLs as they are allowed in domain names.
[1]https://stackoverflow.com/questions/119312/urls-dash-vs-underscore