As many of you's may have noticed at one point or another, some websites use the prefix of www and some don't. So what's the difference and what does it mean?

Basically, there are no differentiating factors between the two. But in an SEO sense, it's vitally important that only one address is used and that the website isn't accessible via both. While this may not apply to a large majority of websites using a modern CMS, it does occasionally apply to pure HTML-based sites.
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