What is a Premium Domain?

It's an english domain name potentially having a high sale value.

Our research indicates that it should meet the following specifications:
A maximum composition of five sequential and meaningful words, in context.
Length SHOULD not exceed 21 characters.
SHOULD not contains numeric characters (0-9).
Does not contain hyphens.
Is not a typographical error or "typo".
Consists of generic words or terms.
For the .COM TLD (other TLDs, ccTLDs and gTLDs etc. have higher requirements):
Full word(s) sequence must be referenced > 150,000 times in Yahoo.
Full word(s) sequence must be searched > 500 times monthly in Overture.

Valuation:

Domain valuation for the certification is based on the following metrics:
Domain name length, number of syllables, readability.
Term frequency.
Keyword search popularity.
Domain extension.