What is linear regression?
Linear regression is an approach for modeling the relationship between and independent and dependent variables.  It is a linear relationship that is described by a positive, negative, or a 0 slope.  The slope describes the velocity of the relationship being measured by the Linear Regression.  The variables measured using linear regression have to be continuous.  If any of your measurements are discrete you can take a log transform of those variables into order to make then continuous and be able to use Linear Regression.