The letter r represents the sample correlation coefficient .The Pearson product-moment correlation coefficient, also known as r, R, or Pearson's r, is a measure of the strength and direction of the linear relationship between two variables that is defined as the covariance of the variables divided by the product of their standard deviations.
The sample correlation coefficient value r is 0 given,so there is no linear relationship between the 2 variables that is the body temperature and head circumference.