Question

A deviation from the specified or expected behaviour that is visible to end-users is called

Answer 1

A deviation from the specified or expected behavior that is visible to end users is called an error.

An error is basically a condition which states that something has occurred wrong.

An error is a wrong action  .

An Error also occurs when a wrong assumption is made and it is also visible to the end user.

Answer 2

A deviation from the specified or expected behaviour that is visible to end-users is called a failure.

The key is a failure after any software or tool is released as well as in Live to end-users with deviation from any specification. As a result, both the testing and development team never perform the task properly as well as quality hugely lacks in software.