There is a lot of lingo exclusively used amongst SEO/SEM professionals. It can sometimes get confusing trying to make sense of all the jargon.

Here is an A to Z list of some of the most common terms in the SEO/SEM industry:

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Glossary:

0 – 9

Some poorly developed content management systems return 200
status codes even when a file does not exist. The proper
response for file not found is a 404.

See also:

• 
  W3C HTTP 1.1 Status Code Definitions