I just discovered this site, and I had a question that has been bugging me for a while. My question isn't so much about a concept as it is about terminology, so I thought I'd check whether this kind of question is acceptable on the site before I ask it.
As an example, here is the question I intended to ask:
My statistics professor claims that the word "correlation" applies strictly to linear relationships between variates, whereas the word "association" applies broadly to any type of relationship. In other words, he claims the term "non-linear correlation" is an oxymoron.
From what I can make of this section in the Wikipedia article on "Correlation and dependence", the Pearson correlation coefficient describes the degree of "linearity" in the relationship between two variates. This suggests that the term "correlation" does in fact apply exclusively to linear relationships.
On the other hand, a quick Google search for "non-linear correlation" turns up a number of published papers that use the term.
Is my professor correct, or is "correlation" simply a synonym of "association"?