noun
advance screening; preview; private showing
A pre-release film screening, often for press, invited guests, or contest winners. Not a public commercial showing.
試写会に当選したので、公開前にその映画を見られる。
I won a ticket to the advance screening, so I can see the movie before its release.
マスコミ向けの試写会が明日
A press preview will be held tomorrow.
上映会 is a broader term for any organized film screening, including public events, retrospectives, or community showings, not necessarily pre-release.
Compound of 試写 (test screening) + 会 (gathering, event). The term is transparently derived from its components.