Definition - What does Showstopper Bug mean?
A showstopper bug is a hardware or software bug that causes an implementation to stop and become essentially useless. This critical bug must be fixed for the development process to proceed further. The term "showstopper" is used in an opposite manner to its classic theatrical usage, which describes something that is strikingly good.
The name itself specifies that every activity stops then and there, and, unless the bug is resolved, the process cannot go on.
Techopedia explains Showstopper Bug
There are various scenarios when a showstopper bug can arise. For example, a customer needs to perform a credit card payment online. The customer enters the billing page, fills up the required details and then clicks on the "Submit" button. The expected result would be a page that says "transaction successfully completed," thanking the customer. However, sometimes, instead of showing the expected page, the system throws an error such as a "Web server" error or a "page not displayed" error. This critical error would then be logged as a showstopper as the customer is left with no workaround to continue with testing the billing page.
Another good example of a showstopper bug can happen during the login process of any application. For example, a user is trying to log in to his/her online email account using a valid username and password. However, the system throws an error even if the user entered the correct details and does not let the user proceed to the next step. This is a showstopper scenario.
Whenever testers discover a showstopper issue, they are responsible for logging the defect and informing the corresponding development team to resolve the issue at the earliest opportunity. Generally, showstopper bugs are raised as P1 or highest priority. Testers usually try to find showstopper bugs before a product release, as they can delay the product release for days, or even weeks, if not handled properly.