What is difference between a Black hole and a Quasar ?
Quasars are visible in the electromagnetic spectrum. Black holes are not.
The word quasar is a joining of the 2 words Quasi and stellar. Quas-ar.
The word quasi is defined as "weird".
They were named this because of anomalies in the data that scientists have collected about them that conflict with the standard theory of cosmology.
From Wiki: The strange spectral lines in their radiation, and the speed of change seen in some quasars, suggested to many astronomers and cosmologists that the objects were comparatively small and therefore perhaps bright, massive and not far away; accordingly that their red-shifts were not due to distance or velocity, and must be due to some other reason or an unknown process, meaning that the quasars were not really powerful objects nor at extreme distances, as their red-shifted light implied.
Quasars' luminosities are variable, with time scales that range from months to hours. This means that quasars generate and emit their energy from a very small region, since each part of the quasar would have to be in contact with other parts on such a time scale as to allow the coordination of the luminosity variations that coincide with the max speed of electromagnetism.