Correlation is a statistical measure that describes the relationship between two variables. It measures the strength and direction of the linear relationship between two or more variables. A correlation of +1 indicates a perfect positive relationship, a correlation of -1 indicates a perfect negative relationship, and a correlation of 0 indicates no relationship between the variables. Correlation analysis is widely used in various fields of research, such as psychology, sociology, economics, and biology, to understand the relationship between variables and to make predictions based on those relationships.