fromEnglish Grammar Today
We can put two noun phrases (np) together to refer to the same person or thing. This is called apposition:
I report to[NP1]Frank Stein,[NP2]Vice-president of marketing, with whom I meet weekly.
[NP1]John Tebbitt,[NP2]a newcomerto marathons, ran a very good race.
Punctuation
Noun phrases in apposition are normally separated by commas in writing (see the examples above). Where the second noun phrase identifies the first, commas are not necessary:
[NP1]My brother[NP2]Rogerlives in New Zealand but[NP1]my brother[NP2]Kevinnever left home.
(RogerandKevinidentify which brothers the speaker or writer is referring to.)
See also:
Apposition
Noun phrases