how two variables relate to each other

The measure of the linear relationship between two variables. Can be positive or negative, depending on which side of the bed it woke up on.

If this is present, then there is an apparent trend in bivariate data. Correlation is generally positive or negative.

A relationship between two variables. They can be low or high, negative or positive, but if two things are correlated, they are more than just casual acquaintances.

When two variables we've measured have some kind of association or relationship between them. It can be positive, negative, or not exist. The last one is the most depressing, naturally.