1. a reciprocal relation between two or more things
2. a statistic representing how closely two variables co-vary; 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. 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
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.