Epidemiological means “about epidemiology” — and epidemiology is the study of how diseases move through groups of people, who gets ill, why, and what might slow the spread. So an epidemiological study, map, or report looks at patterns in a population, not at one patient’s body on the table. You will hear it in news about outbreaks, vaccines, and public health. It is a long, formal, scientific adjective. The related noun epidemic is the outbreak itself; this word is the “how we study and describe the spread” word. It does not, by itself, mean “very contagious”, though people sometimes stretch it that way in loose talk.