The basic plot of a story or group of stories(noun)
A group of stories sharing a plot(noun)
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Use "plotline" in a sentence
"The use of stories to further the main plotline is interesting and I really enjoyed them."
"Some of the themes that Erikson tackles resonate with those from the previous books: convergence, question of fate and the battle of free will vs. predetermination, … The main plotline is built around a certain prophecy, which is at once vague as well as ever-present."
"The plotline is pleasantly, pulpily thin: college kids invade a sun-and-sex spring break spot, a volcanic eruption unleashes a swarm of flesh-eating prehistoric piranhas."