What is the differences between ww or www domain name?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Amresh Kumar: Hello #SEO Specialist Need Help... ;
  I want to know that what is the differences between ww or www domain name. And what are the benefits, tactics, techniques of using ww in domain name.
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  Jim Munro: I am not an expert, Amresh, but as far as I know the only usefulness is when used with a 301 to deal with typos. We use it for sites like ww(dot)shopsafe(dot)com(dot)au which redirect to the corresponding page on www
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  Johan Enblom: Agree, that would be the benefit. Just make sure that only one version is indexed. 
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  Dave Elliott: i tend to use www. as my primary. In my opinion more people are used to it. if most people are trying to get to the nike site i would assume they do www.nike.com rather than just nike.com.
  
  I have nothing to back this assertion up.
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  Amresh Kumar: +Jim Munro ; i am also so don't worry .. and i am  ;confused that if we are using 301 redirect so what's the benefits because my site is index as a www so other people doing this only ww so ...
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  Jim Munro: As long as it is always 301 to the primary site, Amresh, there is nothing to be concerned about. It's only there to catch a few typos, it will not ever benefit you otherwise, so there's nothing to get excited about either. :) ;
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  Amresh Kumar: +Dave Elliott ;i think so it's a critical to find relevant ans. and i have checkd www.nike.com and they are not using any redirect or site index as a www domain. but i want to know what are the differences between www or ww domain name .. but thanks for your suggestion... ;
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  Amresh Kumar: +Jim Munro ;okay so why people using ww only in his domain if there is no benifits. i have searched to many but i can't get any relevant result .. so i think you would be more clear about this....
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  Jim Munro: Be careful of following big brands as your SEO guide, Amresh. Some of them are notorious cheats and others are on the other side of hopeless. They can get away with it, you can't.
  
  I said it above but I will repeat for clarity. The only reason for setting up a ww or a wwww subdomain is to redirect to your www site. You would do this because some people accidentally type ww or fail to pick up the third w with a copy and paste. There is no other reason to do it that I know of.
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  Amresh Kumar: +Jim Munro ;Thank you very much for clarify my doubts and  ;i will keep remain your words in my mind if in future i will see this kind of things .. so thank you so much... ;