Neoplatonism is a modern term used to designate a tradition of philosophy that arose in the 3rd century AD and persisted until shortly after the closing of the Platonic Academy in Athens in AD 529 by Justinian I. Neoplatonists were heavily influenced by Plato, but also by the Platonic tradition that thrived during the six centuries which separated the first of the Neoplatonists from Plato.
In defining the term "Neoplatonism", it is difficult to reduce the school of thought to a concise set of ideas that all Neoplatonic philosophers shared in common. The work of Neoplatonic philosophy involved describing the derivation of the whole of reality from a single principle, "the One". While the Neoplatonists generally shared some basic assumptions about the nature of reality, there were also considerable differences in their views and approaches, and so it can be difficult to summarize the philosophical content of Neoplatonism briefly. Instead, the most concise definition of Neoplatonism casts it as an historical term. It refers to the dynamic philosophical tradition that Neoplatonism was over the course of its history: to the work of Plotinus, who is traditionally identified as the founder of Neoplatonism, and to the many thinkers after him, who developed, responded to and criticized his ideas.