English to English noun
1 
a reciprocal relation between two or more things   source: wordnet30
2 
a statistic representing how closely two variables covary; it can vary from 1 (perfect negative correlation) through 0 (no correlation) to +1 (perfect positive correlation)   Example: what is the correlation between those two variables?
source: wordnet30
3 
a statistical relation between two or more variables such that systematic changes in the value of one variable are accompanied by systematic changes in the other   source: wordnet30
4 
Reciprocal relation; corresponding similarity or parallelism of relation or law; capacity of being converted into, or of giving place to, one another, under certain conditions; as, the correlation of forces, or of zymotic diseases.   source: webster1913
