The correlation between two random variables is a measure of how closely they relate. It may be a positve correltaion if they increase together or a negatuve correlation of one goes down as the other goes up. the term is sometimes used in this general way, but in {{statistics}{ it refers the the linear relationshiop between variables, that is the extent to which two variables, say x and y, lie close to a line y=mx+c for some values of m and c.
Used on Chap. 12: page 284
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