Owen: Have you ever heard of the Gnostics? Annie: Is that when you're not sure if God exists, like not quite an atheist? Owen: No. Jesus' disciples, they all wrote gospels, right? But they didn't all make it into the Bible. The church only wanted the ones that told the story they were trying to tell.
Annie: I didn't know that. Owen: Well, the same goes for all history. Same goes for your brain. Annie: What do you mean? Owen: Our brains are just computers that make our life stories make sense.
Gnosticism" was a pejorative, and polemical, term to describe various, numerous sects which emerged out of early Christendom but parted ways with the Advent of cannonical Christianity via The Roman Catholic Church. They held onto teachings and texts which were and are deemed apochrophyl and heretical as such. The negative connotations around the "Gnostics" have stubbornly persisted, and were formed prior to the resurfacing of The Dead Sea Scrolls and Nag Hammadi libarary - which contain an accurate and historical account of what exactly those groups believed and were up to.
"Gnosticism" as as term is about as useless as "Hinduism" - no such thing. These are big, broad, brush bastardizations used to describe "others", and in the case of The Gnostics the intention was to vilify. These various groups shared many core ideas in common but were hardly monolithic. And not all of these "gnostic" ideas, as it were, are necessarily exclusive to those early Christiain sects, as quite a bit of overlap exists between them and groups such as The Bodhisattvas of Mahayana Buddhism, The Sufis, The Manicheans, and The Yazidis (who are currently in the midst of a modern day genocide) among others. Genocide is a long running theme among gnostic sects, in a way the Witchhunts began with them - the last known Cathar was burned at the stake in the early 1300's.