Research papers will mention a variety of different variables, and, at first, these technical terms might seem difficult and confusing. But with a little practice, identifying these variables becomes second nature. Because they are sometimes not explicitly labeled in the research writeup, it is useful to have a real research paper on hand as you learn these terms, so you can get some hands-on practice at identifying them.
The independent variable, also known as the IV, is the variable that the researchers are manipulating in an experiment or quasi-experiment. It is also the label given to the "criterion" variable in certain types of regression analysis. For example, if a researcher has two groups of people watch either a happy film or a sad film before giving an IQ test, the IV is the mood of the participants.
The dependent variable, or DV, is the one that is being measured by the researcher; it is the outcome variable. There is often confusion between the IV and the DV among new science students, but a good way to distinguish them is to remember that the outcome of measuring the DV is hypothesized to depend on the manipulation of the IV. In the above example, IQ was hypothesized to depend on the mood of the participants.
A covariate is a variable that the researchers include in an analysis to determine whether the IV is able to influence the DV over and above any effect the covariate might have. The classic example is when researchers take a baseline measurement, perform some manipulation, then take the measurement again. When they analyze this data, they will enter the baseline scores as a covariate, which will help cancel out any initial differences between the participants.
An extraneous variable is a little different from the rest because it is not directly measured, or often even wanted, by the researchers. It is a variable that has an impact on the results of the experiment that the researchers didn't anticipate. For example, the heat of the room might be different between two groups of IQ tests, and the hot room might annoy people and affect their scores. Scientists try to control these variables, which means keeping them constant between groups.