From The Gnostic Bible:

Scholars of ancient and late antique religions have attempted to sort through the issues of definition and taxonomy in order to reach some clarity regarding gnosis and gnosticism. In 1966 many of the leading scholars of gnosis gathered at an international conference in Messina, Italy, and produced a set of statements that are meant to define gnosis and gnosticism. Gnosis, they maintain, is “knowledge of the divine mysteries reserved for an elite,” and this is a term of very broad application. On the other hand, gnosticism is “a coherent series of haracteristics that can be summarized in the idea of a divine spark in man, deriving from the divine realm, fallen into this world of fate, birth and death, and needing to be awakened by the divine counterpart of the self in order to be finally reintegrated.”2 Gnosticism is thus a religious movement represented by religious groups that emerged in the second century CE and after, especially within the context of Christianity, groups such as the followers of Basilides and Valentinos, two particularly significant early Christian teachers of gnostic religion.