In most dictionaries and grammars, 'noun phrase' is defined by the function it performs, i.e., a subject, an object or a predicative complement. But this definition is not quite helpful considering this from CGEL*:
In addition to their prototypical function as complements in clause structure, NPs may appear with a number of other functions, including the following:
 i I was talking [to the doctor]. [complement in PP]
ii I like [Sue’s analysis of the passive construction]. [subject-determiner in NP]
iii Fred arrived the day before yesterday. [adjunct in clause]
iv The nail was [three inches long]. [modifier in AdjP]
v Fred arrived [a whole day late]. [modifier in AdvP]
vi The wreck was discovered [a mile under the sea]. [modifier in PP]
vii She was writing a treatise on [the opera ‘Carmen’]. [modifier in NP]
viii I finally met his wife, a distinguished anthropologist. [supplement]
ix Elizabeth, your taxi is here. [vocative]
The 'function' of 'noun phrase' discussed by most dictionaries and grammars is its syntactic function, which, as is shown above, can be quite messy and therefore doesn't really help neatly define 'noun phrase'.
Fortunately, there is another function of 'noun phrase' that is not syntactic. In any given sentence, 'noun phrase' refers to something, be it concrete or abstract or animate or inanimate.
For example, in [6i] above, the doctor refers to a specific person who was a doctor and was being talked to by me. Similarly, in [6iii], the day before yesterday refers to a specific day when Fred arrived. And so on.
In essence, what a noun phrase refers to in a given sentence can be any concrete object(s) or any abstract concept(s) or any animal(s) or any inanimate thing(s).
If you're to use a single term to describe what a noun phrase can refer to in any given sentence, what can it be?
Please note that that term should be able to encompass "any concrete object(s) or any abstract concept(s) or any animal(s) or any inanimate thing(s)".
I was thinking about 'object' and 'thing', but the problem is, 'object' has the nuance of excluding abstract concepts, and 'thing' has the nuance of excluding animate objects.
*The Cambridge Grammar of the English Language by Pullum (p 327)