"Hellenistic" is a modern word and a 19th-century concept; the idea of a Hellenistic period did not exist in Ancient Greece. Although words related in form or meaning, e.g. Hellenist (Ancient Greek: Ἑλληνιστής, Hellēnistēs), have been attested since ancient times, it was J. G. Droysen in the mid-19th century, who in his classic work Geschichte des Hellenismus, i.e. <answer>History of Hellenism</answer>, coined the term Hellenistic to refer to and define the period when Greek culture spread in the non-Greek world after Alexander’s conquest. Following Droysen, Hellenistic and related terms, e.g. Hellenism, have been widely used in various contexts; a notable such use is in Culture and Anarchy by Matthew Arnold, where Hellenism is used in contrast with Hebraism.
What does Geschichte des Hellenismus mean?
History of Hellenism