A "story concept" refers to the central idea or premise that a story is based on. It captures the main theme, plot, or message that the writer wants to convey. Full definition
It attempts to expand on the same story concepts with a different gameplay dynamic. (gearnuke.com)
What I received was a sequel that added a great deal of content and interesting new story concepts, while fixing most of the issues the first game had. (monstervine.com)
They could have had a great story concept but they kinda failed with it, well failed isn't the right word, they didn't even try. (lifeisxbox.eu)