The term nominal phrase, rather than noun phrase, is used because grammatical structures other than nouns -- such as gerunds and infinitives -- are often found in these noun positions. For example, “To ignore the evidence is impossible.” The infinitive phrase “to ignore the evidence” is functioning as the noun in this sentence. Similarly, in the sentence “Mike and Cindy enjoy jogging through the park,” “jogging through the park” is a gerund phrase functioning as the direct object of the verb “enjoy.”
Considered an optional nominal slot is the appositive phrase. An appositive is a noun phrase that provides more, and often unnecessary, information regarding another more pertinent nominal. The grammatical stability of the sentence does not depend on the appositive. For example, “The pilot, an Air Force veteran, flew the plane with precision.” The appositive phrase “an Air Force veteran” provides additional -- but not necessary -- detail regarding the sentence’s subject, “the pilot.”