Essenes
A separatist community usually credited with the Dead Sea Scrolls — and the New Testament never once mentions them.
The Essenes are described by Josephus, Philo and Pliny as a strict, communal, celibate movement that withdrew from the temple establishment. They are generally connected with the settlement at Qumran and the scrolls found in the caves above it, which is the largest single find of pre-Christian biblical manuscripts. The striking thing from a New Testament point of view is their total absence from it: the gospels name Pharisees, Sadducees, Herodians and Zealots, and never these.
Not a word scripture uses. The word never appears in the Bible. Everything known about them comes from Josephus, Philo, Pliny the Elder and the Qumran scrolls, and even the link between the Essenes and Qumran is an inference rather than a statement.