Definition of an Epic
An Epic refers to a cohesive unit of work that is too large to complete within a single Sprint. Epics represent larger initiatives within your product or project. The work associated with an Epic is also broken down into Product Backlog items to make it manageable for implementation.
Note: Epics are not part of the Scrum framework and this can be explained. Scrum focuses on creating value during each Sprint.
Drawbacks
When the scope of work is too large to finish within a Sprint, you run the risk that your team does not produce an Increment. Consequently there is a delay in your “inspection and adaptation” cycle and you also risk unwanted deviations occurring. Additionally, your predictability decreases.
Holistic view
How can you use Epics then? Particularly Product Owners use them to create a holistic view and to prioritize better. They do this for example, with the help of Jira, a tool that helps Scrum Teams organize and manage work.