  The quark-gluon plasma, possibly created in ultrarelativistic heavy-ion
collisions, is a strongly interacting many-body parton system. By comparison
with strongly coupled electromagnetic plasmas (classical and non-relativistic)
it is concluded that the quark-gluon plasma could be in the liquid phase. As an
example for a strongly coupled plasma, complex plasmas, which show liquid and
even solid phases, are discussed briefly. Furthermore, methods based on
correlation functions for confirming and investigating the quark-gluon-plasma
liquid are presented. Finally, consequences of the strong coupling, in
particular a cross section enhancement in accordance with experimental
observations at RHIC, are discussed.
