Definition of "correlation" []

• A causal, complementary, parallel, or reciprocal relationship, especially a structural, functional, or qualitative correspondence between two comparable entities: a correlation between drug abuse and crime. (noun)
• Statistics The simultaneous change in value of two numerically valued random variables: the positive correlation between cigarette smoking and the incidence of lung cancer; the negative correlation between age and normal vision. (noun)
• An act of correlating or the condition of being correlated. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Historically, the dependency between two securities has been calculated using linear correlation or more generically “correlation."
• "It is significant that in later times the term correlation has come to be applied more especially to the purely empirical constancies of relation, and has lost most of its functional significance."
• "Except the correlation is the exact opposite of conventional wisdom -- the economy crashes after tax cuts and takes off after tax increases."