Hi
a domain can be labeled as premium, either by the registry, the aftermarket platform or by any seller in a sales thread.
however, that doesn't necessarily mean that it is a premium domain, like prime steak is premium cut.
premium domains, speak for themselves, they really don't need the label.
since registrars have "partnered" with or taken over some aftermarket platforms, then many names listed on these venues will show up as Available "Premium Priced" in the query results for the keywords you enter...if/when you search for a random domain name.
and again, it may say premium, but only you can decide if the price is worth the name
brandables, in todays age, can be any turd domain that's relatively short and preferably .com
just like "pronounceables", which are as vague, as brandables.
read thru same of the sales threads here , that have such labels in description and decide which are and which are not what they claim
though trying to understand them, in a black and white scenario is impossible for a newbie.
imo...