In research, an "experimental unit" refers to the smallest division of experimental material to which a treatment is applied. This could be an individual subject, such as a mouse in a laboratory study, or a group of subjects, like a classroom of students in an educational experiment. The choice of experimental unit is crucial because it affects the design and analysis of the study. Understanding experimental units helps researchers ensure that their results are valid and reliable. By clearly defining these units, scientists can accurately measure the effects of different treatments or interventions, leading to more meaningful conclusions. Proper identification of experimental units also aids in avoiding biases in the results.