I looked up
gnosticism on wikipedia which has more details but I think the video below does a better job of explaining gnosticism in the context of western culture. (The wikipedia article reads like a list of facts accumulated by people who don't understand them in a wider context ... which might be a problem with wikipedia in general.)
(I like the youtube channel this video comes from. The author is seminary professor so the videos are somewhat academic but they hold my interest well enough unlike other academic videos I've viewed.)
Gnosticism and the Early Church
From the video (not direct quotes):
Gnostic fundamentals:
The world isn't real
The world is unpleasant ("evil"), and was not created by God but by a lesser being. The spiritual realm is superior to the physical realm.
Elitist - gnostics don't try to spread their ideas.
Gnosticism was not an actual well defined religion
Gnosticism did not pre-date Christianity
Christianity did not borrow from gnosticism.
There is no single set of beliefs that are "gnostic"
"Gnostic" describes trends or impulses.
Examples: "You do not have a soul, you are a soul that has a body" This is an example gnostic thinking it is not consistent with Christian teaching in which God created man in His image. It denies the reality of the physical. Any kind of pursuit of ascetic practice in pursuit of spirituality being superior to the mundane is also "gnostic".
In the move "Star Wars", when yoda says "Luminous beings we are... not this crude matter, that is a gnostic point of view.
For most of history all that was known of gnosticism was from books that rejected it. It was only relatively recently that actual gnostic texts were found.
Gnostics believe a set of views related to the created world, salvation, and the life of a believer.
Salvation comes from an ascetic life style.