What is "berossus"

Berossus or Berosus (; name possibly derived from , " Bel is his shepherd"; ) was a Hellenistic-era Babylonian writer, a priest of Bel Marduk and astronomer who wrote in the Koine Greek language, and who was active at the beginning of the 3rd century BC. Versions of two excerpts of his writings survive, at several removes from the original.