Final answer:
The punctuation formula np stands for noun phrase, which functions as a noun. An appositive is a noun or phrase that describes another noun.
Step-by-step explanation:
In punctuation, the formula np stands for noun phrase, which is a group of words that functions as a noun. It can be as short as a single noun or as long as a full sentence. For example, in the sentence The big, red dog, The big, red is the np.
An app is short for appositive. An appositive is a noun or noun phrase that renames or identifies another noun before it. It provides additional information or specifies which one is being referred to. For example, in the sentence My friend John, a talented musician, played the piano, a talented musician is the appositive that further describes John.