There are no official designations or grammatical terms for "positive noun" in the English language. The phrase could be a misnomer for "possessive nouns," or an unrecognized phrase used to describe nouns that may have positive attributes.
With the exception of pronouns, possessive nouns show possession and often appear with an apostrophe. For example: "the butler's room," "my mother's" and "Bob's Tires." While regular plural nouns do not use an apostrophe, plural possessives do, though usually after the "s" that signifies plurality.
Referring to a noun that describes something thought to have positive traits as a "positive noun" would be inaccurate. The main issue with this is that positive designations are highly subjective; they are not the same for everyone. Additionally, adjectives are generally used to apply attributes to nouns.