Dashes vs. Underscores In SEO
You should use dashes, -, instead of underscores, _, generally when it comes to urls in seo. If you have term1-term2 in a url, then the search engine will see these terms as the following: term1, term2, term1 term2, or term2 term1. This is must more friendly to search engines. The exception to using dashes is if you have a term like _MAXINT, which may be different from MAXINT in programming languages. In reality though, Google has made adjustments for dashes and underscores, so that you can use them interchangeably with some respect. It is possible for Google to make a mistake in parsing your url terms if you use underscores, thus it is safer to use dashes to avoid any problems. These are the differences in how search engines view dashes and underscores, and the reasons that dashes are better to use in normal circumstances.
Having devoted considerable time to this question during my career, particularly in recent years, I can only conclude that dashes are not the best delimiter. Moreover, I believe a consensus will emerge eventually with an alternative character being used universally — probably the underscore