Can correlation be used to describe a curved relationship between variables, or only the strength of a linear relationship between two variables?

In general, would you use correlation to completely describe two variable data?

In your own words how do you define a regression line, and what is it used to do?

Specifically, comment on what a least-squares regression line is.

How is regression different than correlation?

What does the square of the correlation, r², signify? What does an r² value of 1 mean?

A prediction is only as good as the correlation it is based on. Explain, use an example of your own about a variable you are interested in.