  The present article reviews facts and problems concerning charge hadron
production in high energy collisions. Main emphasis is laid on the qualitative
and quantitative description of general characteristics and properties observed
for charged hadrons produced in such high energy collisions. Various features
of available experimental data e.g., the variations of charged hadron
multiplicity and pseudo-rapidity density with the mass number of colliding
nuclei, center-of-mass energies and the collision centrality obtained from
heavy-ion collider experiments are interpreted in the context of various
theoretical concepts and their implications. Finally, several important scaling
features observed in the measurements mainly at RHIC and LHC experiments are
highlighted in the view of these models to draw some insight regarding the
particle production mechanism in heavy-ion collisions.
