The question in SEO(Search Engine Optimazation) URLs is whether to use a hyphen, or dash, (these-are-hyphens) or an underscore (these_are_underscores) to separate your words.
Does Google recognize both of them as word separators?
The short answer is that you should use a hyphen for your SEO URLs. Google treats a hyphen as a word separator, but does not treat an underscore that way.
Google treats and underscore as a word joiner — so mahtab_alam is the same as mahtabalam to Google. This has been confirmed directly by Google themselves, including the fact that using dashes over underscores will have a (minor) ranking benefit.
Again, SEO URLs should use hyphens to separate words. Do not use underscores, do not try to use spaces, and do not smash all the words together intoonebigword. As of 2012, dashes are still the best way to optimize your SEO URLs.
For example
Use mahtab.com/mahi-alam
instead of mahtab.com/mahi_alam
when you create a new project or website
Thanks
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