Premium domain names,
Premium domain names are names already registered by the internet hosting provider or domain registrar, a premium domain name is a with godadday is not a premium domain name with 1and1 internet Inc. This is why you see a domain as premium with one registrar but taken or not available with another domain registrar. Domain name registrar are also domainers, they search and pick domain name to sell in their potential visitor.
Premium domain names are mostly valuable domain name, they are mostly short, memorable and has general market liquidity and hence, their higher prices.