The phrase "is holiday song" is a verb phrase that functions as a predicate. It is not a single part of speech but a grammatical construction composed of a verb and a noun phrase.
The primary component is the verb "is," the third-person singular present indicative form of the linking verb "to be." This verb connects a subject to a subject complement. The subject complement here is the noun phrase "holiday song." Within this noun phrase, "song" is the head noun, and "holiday" is a noun functioning as an attributive adjective (or noun adjunct), which modifies "song" to specify its type or theme.
For analytical purposes, the crucial element is its predicative function. The phrase makes an assertion of identity or classification about a subject (e.g., "[Subject X] is a holiday song"). While the omission of the indefinite article "a" makes the phrase ungrammatical in formal prose, its structure is common in search queries and data strings. Therefore, the main point for an article using this keyword would be its role in classifying or defining a subject within a clause.
