The www Subdomain in a Domain Name

In ancient times, when domains had just appeared, the letters www (an abbreviation for World Wide Web) were added before the domain name. That is, the site was called not site.com, as is common now, but www.site.com.

Then the letters www gradually disappeared from use, and the site www.site.com is now considered a subdomain of the site.com site. That is, a subdomain in the sense that there can be completely different information there in relation to the main site.

In practice, however, no one does it this way. In real life, both the domain with www and without it host the same site. However, text duplication is extremely harmful for promotion in search engines. Therefore, in practice, they do the following:

They declare one of the name variants as the main one (usually without www). And on the second name variant, they set up a redirect to the main variant, thereby performing canonicalization.

We will study how this is done in advanced lessons. For now, just be aware of the existence of such a problem.