Final answer:
In an experiment, a variable is a condition that can change and affect the outcome. The dependent variable is affected by the independent variable, which is controlled by the researcher.
Step-by-step explanation:
A variable is any condition that can change and that might affect the outcome of an experiment. In the context of an experiment, there are several types of variables. The dependent variable is the variable in a scientific experiment that is affected by another variable, known as the independent variable. The independent variable is the one that the researcher changes or manipulates to observe the effects on the dependent variable. Other factors that might affect the outcome, such as constants and control variables, should be kept stable to ensure a fair test. It's also essential to differentiate these from a placebo, which is a substance with no therapeutic effect used as a control in testing new drugs, or to measure the effects of participant expectation.