In Big O, common notations have common names (instead of saying, Oh of some constant factor):O(1) is ConstantO(log n) is LogarithmicO(n) is LinearO(n^2) is QuadraticO(n * log n) is ???Is it just n log n or does it have a special name like the above?
What is the name the class of functions described by O(n log n)?
terminology;asymptotics
It's called linearithmic time, and is a special case of a more general class known as quasi linear.  As the name may suggests, the algorithms that fall in this class almost run in linear time; in fact they have a lower complexity than algorithms which run in $O(n^k)$ with $k > 1$.