A negative correlation is said to exist when as one covariate increases the other covariate decreases. An excellent example of a negative correlation would be number of hours spent socialising by a group of students and their eventual examination mark. Going out too much seriously jeopardises your examination success.
Found on http://www.gerardkeegan.co.uk/glossary/gloss_a.htm
A relationship between two variables where higher values on one variable tend to be associated with lower values on the second variable; sometimes referred to as an inverse relationship (e.g. age of non-vintage cars and their market value).
Found on http://www.bath.ac.uk/catalogues/information/glossary/