Which of the following best defines an acronym?

The definition of an acronym is accurately captured by the choice indicating that it is a word formed from the initials of other words. This process involves taking the first letters of a series of words and combining them to create a new term. Common examples include NASA (National Aeronautics and Space Administration) and NATO (North Atlantic Treaty Organization). Acronyms are typically pronounced as words themselves, differentiating them from initialisms, where the letters are pronounced individually.

Exploring the other options, the choice regarding multiple meanings refers to polysemy rather than acronyms. Formal writing, while it may incorporate acronyms, does not define them, and the idea of a compound word with no clear meaning does not align with the established understanding of what constitutes an acronym. Thus, selecting the option that describes an acronym as a word formed from initials is the most accurate and precise choice.