This is... quite wrong? The dictionary says:
1. a mutual relationship or connection between two or more things
2. [Statistics] interdependence of variable quantities.
3. [Statistics] a quantity measuring the extent of the interdependence of variable quantities.
The most sympathetic to your definition is Wikipedia:
In statistics, correlation or dependence is any statistical
relationship, whether causal or not, between two random variables or bivariate
data. In the broadest sense correlation is any statistical association, though
it actually refers to the degree to which a pair of variables are linearly
related.
And that's the
mathematical formulation. Correlation also has a meaning in everyday speech, and mathematics doesn't have the authority to just adopt terms and then claim people are wrong after they've changed the meaning.
Also correlation very definitely means that knowing <x> tells you something about <y>. And vice versa. Like, for example: its value. Or at least a better idea of it than pure guessing without correlation.
Also correlation very definitely means that knowing <x> tells you something about <y>. And vice versa. Like, for example: its value. Or at least a better idea of it than pure guessing without correlation.