R is the correlation coefficient.
R^2 has a much longer (and more difficult to remember....) title!!!!!!!!
Why does this piss me off? Because I have had MULTIPLE instances of methods or protocols asking for the 'correlation coefficient' to be calculated and compared to a criteria... and strangely enough, I calculate the correlation coefficient and get told to recalculate it later, because, of course, these people really wanted R^2. Worse yet, if the correlation coefficient is actually NEGATIVE, I have trouble comparing it to a critera that really wanted R^2 (a positive number)
When they ask for 'correlation coefficient (R2)' I am left wondering which one they REALLY wanted.....