Evolution of the concept of Quark Matter : the Ianus face of the heavy ion collisions

Since the beginning of the quest of quark matter deep changes have developed in our concept in understanding its properties. In Table 1 the ideas are collected, which dominated at the beginning of quark matter research. The present status of these ideas are also displayed. Although theoretical models supported the early concept, but the experimental data forced to change these speculations step by step. Thus the picture of a static, weakly interacting gaseous quark-gluon plasma was substituted by the more dynamic, strongly interacting fluid-like quark-gluon matter, where the ingredients gained an effective mass during the intense microscopical interactions.