Correlation is a statistical technique that can show whether and how strongly pairs of variables are related. For example, height and weight are related; taller people tend to be heavier than shorter people. Correlation can tell you just how much of the variation in peoples' weights is related to their heights.
Correlation always does not signify cause and effect relationship between the two variables. As Correlation is a statistical measure that describes the size and direction of a relationship between two or more variables. This is also referred to as cause and effect.