Epic
In plain terms
A large body of work broken into smaller stories.
Going deeper
An epic is a big feature or initiative too large for one sprint, decomposed into user stories. It groups related work under one theme.
Under the hood
Spans multiple sprints; provides a higher-level unit for roadmap planning above stories.
Examples
Large features, story grouping, roadmaps, Jira epics, initiatives.
Think of it like...
Like a whole book broken into individual chapters (stories) you write over time.