There are probably many cases when the tester reported a bug and the developer replied: “This is not a bug. This is a feature …”.
So where does the line go? When is it a bug, and when is it a feature?
What differentiates a fault (bug) in system performance from a feature is a simple criterion: Is there a requirement.
Bug — a result of unwanted code behavior, behavior that conflicts with a requirement.

Please take a look into below examples:
Bug diminishes the value of the product whereas feature improves the value of the product.
Bug occurs when the product does not meet the product specifications or end-users expectations whereas a feature is an end-user expectation from the product.
Bug validates a mismatch or failure based on the feature requirements and feature is an application functionality developed for customers. It can be a new requirement or changes in the existing feature

When requirements are not written correctly and clearly, sometimes developers misunderstand them.
The product manager must make sure that the requirement is clear to them, and that the developers does implement what was asked of him.
An optimization proposal / idea for a new feature should be reported directly to the product manager.

And let your product have no bugs, only features.

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