An independent variable is a treatment: something that is varied under your control to test the behavior of another variable.
A dependent variable is something that is measured in response to a treatment.
For example, you might want to test the ability of various promotions to enhance sales of a particular item.
In this case, the promotion is the independent variable and the sales of the item made as a result of the individual promotion is the dependent variable.
The value of the linear regression intercept tells you the predicted value for sales when there is no promotion for the item selected for analysis.