“Epic” is a term used to characterize a large user story that can’t be delivered as defined within a single iteration or is large enough that it can be split into smaller user stories, it was introduced back in 2004 by Mark Cohn in his book “User Stories Applied For Agile Software Development.”. There is no standard form to represent epics. Some teams use the familiar user story formats, while other teams represent the epics with a short phrase.
The great thing about Epics is that they let you save an idea with one backlog item until your team identifies the need to deliver the outcome that the epic enables. At that point, your team can split the epic into smaller user stories during backlog refinement, that way you can track your ideas without stuffing your backlog with multiple items. Epics give you a way to establish a hierarchy for your backlog items in which the Epic represents the original idea, the user stories represent the various aspects of the solution you need to find or the options you have to accomplish a certain objective.
We can also look at the concept of themes used for grouping user stories related to the same topic. this concept is usually used to group user stories that were identified separately together and can help making important decisions by filtering them of sorts to decide what stories to group into a particular sprint or delivery. A few things can go wrong, however, especially when the Teams overcomplicate their use of epics by viewing them as more than just large user stories. This can happen when the team creates difficult mechanisms to differentiate between the two as well as create extensive tools for tracking epics separately from other backlog items. It may also go wrong when Teams try to guess epics even though these items are typically very vague and prone to a great deal of uncertainty, reducing the likelihood of reliable or useful estimates.