In Mathematics, variable is defined as something which varies with the situation. For instance, if I ask you - "What is the temperature today?" You might answer 27 degrees Celsius. But if I ask you after few days the same question, you might answer a different value. Hence, we can say that temperature is a variable.

In a study, independent variables are the ones that are not influenced by other variables. For instance, if there is a study that investigates whether crime rate increases or decreases with unemployment, the independent variable will be unemployment. Here, it is reasonable to assume that if unemployment increases crime rate increases. Hence, we can say that unemployment causes crime rate and not vice versa. Hence, unemployment is independent variable.

Dependent variables are the ones that change due to changes in the independent variable. For instance, in above example, crime rate is dependent variable.