Understanding SEO With Aedig

Root Domains – the domain name you need to buy/register with a TLD extension

Examples of root domains
*.seomoz.org
*.searchengineland.com
*.blogspot.com
*.about.com

Subdomains – the “third level” domain name; these are free to create under any root domain you own/control

Examples of subdomains
www.seomoz.org
searchengineland.com (yes! even without a third-level name it falls under our definition of a subdomain in this application)
postsecret.blogspot.com
southernfood.about.com

Subfolders – the folders behind a domain address

Examples of subfolders
www.seomoz.org/blog/
searchengineland.com/columns/
postsecret.blogspot.com/2009/
southernfood.about.com/library/

Search engines have metrics that they apply to pages, such as PageRank, and metrics they apply to subdomains and root domains (including things like TrustRank, various quality scores, domain level link metrics like Domain mozRank, etc.).

Through years of experience, observation and testing, SEOs have observed some very steady patterns of behavior:

Individual pages benefit from being on powerful subdomains & root domains. This is why if someone copies your personal blog post on the best way to microwave burritos into Wikipedia, that page will rank far better than yours, even with the exact same content (ignoring the duplicate content issues).

Subdomains DO NOT always inherit all of the positive metrics and ranking ability of other subdomains on a given root domain.

Some subdomains GET NO BENEFIT from the root domain they’re on. These include sites like WordPress.com, Blogspot.com, Typepad.com, and many others where anyone can create their own subdomain to begin publishing.

Subfolders DO appear to receive all the benefits of the subdomain they’re on and content/pages behave remarkably similarly no matter what subfolder under a given subdomain they’re put in.

Good internal and cross linking CAN HELP to give share the positive metrics from one subdomain to another (but not always and not perfectly).