What is the meaning of "annual"?

The term "annual" specifically means something that occurs every year. This definition is rooted in the Latin word "annus," which means year. Annual events or occurrences are significant because they are scheduled to take place once during the calendar year, making them a consistent and predictable part of a yearly cycle, such as an annual meeting or an annual tradition.

In contrast, the other options describe frequencies that are different from "annual." Monthly suggests an occurrence every month, which is notably more frequent than yearly. Events that happen once every decade are deemed decadal, and anything described as occasional and irregular does not have any predictable time frame at all. Therefore, "annual" distinctly refers to events that are set to happen each year, confirming the accuracy of the chosen answer.