Which of the following defines an acronym?

An acronym is defined as an abbreviation formed from the initial letters of a phrase. This means that it takes the first letter of each word in a phrase and combines them to create a new word that can be pronounced as a single term. For example, NASA is an acronym for the National Aeronautics and Space Administration, where each letter stands for a word in the longer name. This process of creating acronyms is commonly used to simplify lengthy names or terms, making them easier to remember and use in conversation.

In contrast, the other options do not accurately represent what an acronym is. Describing a noun refers to the function of adjectives, while a conjunction made of two words does not relate to the formation of acronyms at all. Lastly, a punctuation mark signaling a pause concerns grammar rather than word formation. Thus, the correct definition aligns perfectly with the characteristics of acronyms and their function in language.