Which of the following describes a proper noun?

A proper noun is characterized as a specific person, place, thing, or idea that is unique and therefore requires capitalization. This distinction is important in grammar, as it helps to identify and specify particular entities rather than making general references. For example, "John," "Paris," and "Eiffel Tower" are all proper nouns because they denote specific names of individuals and locations that are distinct from common nouns like "man," "city," or "tower." The requirement for capitalization serves to highlight their significance and uniqueness in written language.

In contrast, the other options describe different grammatical concepts that do not fit the definition of a proper noun. A general name for a person, place, or thing refers to common nouns, which denote general items rather than specific ones. An acronym that stands for a specific idea may represent unique concepts or organizations but doesn't inherently dictate proper nomenclature by itself. Lastly, a combination of adjectives and nouns does not identify entities by their unique names and thus does not pertain to the definition of a proper noun.