"In vivo" is a Latin term meaning "within the living." It refers to experiments or studies conducted in living organisms, such as animals or humans, to observe biological processes in their natural context. This approach is essential for understanding how treatments, drugs, or interventions affect living systems. In contrast to "in vitro," which means "in glass" and involves studies in controlled environments like test tubes, in vivo research provides insights into complex interactions within an organism. This method is crucial for fields like medicine, pharmacology, and biology, as it helps researchers evaluate the effectiveness and safety of new therapies.