Final answer:
Subplots are secondary plots in a narrative that typically involve supporting characters, mirroring the main plot's themes and resolving prior to the main plot. They add complexity, provide relief, and support thematic development within the story.
Step-by-step explanation:
A subplot is a secondary plot in a story, often involving supporting characters who have their own personal journeys and conflicts. These subplots echo or mirror the themes of the main plot, but are resolved before it. For instance, in 'Romeo and Juliet,' the subplot involving Mercutio and Tybalt provides background and a minor climax that builds suspense by leading to Mercutio's death, which is resolved before the tragic conclusion of the main protagonists. Similarly, other stories might have sub-climaxes which are turning points for these secondary conflicts and can help to build and release suspense during the rising action of the narrative.
Subplots serve several purposes: they provide depth to the story by fleshing out secondary characters, offer relief from the main narrative, and reinforce the story's themes. They are crucial in making a plot more complex and engaging. The resolution of subplots often leads to the falling action of the main story, moving the narrative towards the climax and eventual dénouement.