Dependent Variable (DV)
In an experiment there are two variables; the independent variable (IV) and the dependent variable (DV). In the most basic sense, you need two variables because as a researcher, you want to be able to examine if something (a drug, a therapy, a teaching technique, whatever) has an effect on some participant (person, people, animals, etc.). To accomplish this, you not only need something to examine (and manipulate - this is the IV), but also something to measure the effect the IV has (this is the DV). Thus, we can define the DV as the variable that is being measured. It is this variable that we, as the researchers, look at for change. IF there is a change, we may conclude that the IV affected the DV. The ultimate here is to establish that the IV caused the change in the DV (this is the magical "cause-effect" relationship).