Which term refers to observable circumstances or occurrences?

The term that refers to observable circumstances or occurrences is "phenomena." This word is commonly used in scientific contexts to describe events or situations that can be witnessed or measured, particularly those that can be analyzed or studied in various fields such as science, philosophy, and the social sciences.

Phenomena are essentially the facts or events that are being observed, as opposed to the interpretations or explanations of those observations. This definition aligns perfectly with the concept of observable circumstances, making this choice the most appropriate answer. Other terms, while related to the study or analysis of phenomena, do not fit the specific definition as well; hypotheses relate to proposed explanations, data refers to the collected evidence or observations, and experiments are systematic investigations designed to test hypotheses or explore phenomena.