n.  1.  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;

Noun  1.  correlation  a reciprocal relation between two or more things Synonyms: correlativity 
2.  correlation  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); "what is the correlation between those two variables?"  
3.  correlation  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 Synonyms: correlational statistics 