The term is a noun phrase. The main point, or head word, of the phrase is the noun "parade." This word identifies the core subject or entity being discussed.
In this construction, the words "Patriots' Day" function collectively as a noun adjunct or attributive noun. Although "Patriots' Day" is a proper noun identifying a specific holiday, its grammatical role here is to modify the head noun ("parade"). It acts like an adjective, specifying the particular type or occasion of the parade, distinguishing it from other events like a "Thanksgiving parade" or a "victory parade."
For the purpose of an article, this grammatical structure is significant. It establishes that the central topic is the event (the parade), while the context or specific theme is the holiday (Patriots' Day). The article's focus should be on the parade itself, with the holiday's name serving as the primary descriptor that defines its purpose and timing.
