A bug is a flaw in software or design that makes a product behave differently than intended, from a crash at checkout to a button that overlaps text. In UX terms, bugs split into two kinds: functional bugs, where the code is broken, and UX or usability bugs, where the code works but the experience is wrong.
Use cases
Bugs are where quality becomes visible. Users never see your clean code, but they see the checkout that fails, and a single bad one can end the relationship.
A payment button works on Chrome but silently fails on Safari. A chunk of customers can't check out, and most leave without reporting it.
An error message says "something went wrong" with no next step. The feature technically works, but the copy is a UX bug that leaves users stuck and blaming themselves.
A typo sits in the product's own name on the homepage. Low severity, high priority, because it's the first thing every visitor reads and it looks sloppy.
How it's used in practice
Separate severity from priority: severity is how badly it breaks, priority is how soon you fix it, and they don't always match.
Write reports someone can act on: steps to reproduce, expected result, actual result, environment, and a screenshot or recording.
Triage together. QA judges technical impact, product and design judge user and business impact, and the two set the order.
Treat UX bugs as real bugs. If the experience is broken, file it, even when the code is "working as designed."
Catch them early. Fixing a bug in production costs far more than catching it in design or development.
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Pro tip: The trap is the bug that's "working as designed." A confusing flow throws no error, so it never lands in the tracker, but users feel it every day. Give your team a way to log experience bugs, not just broken code, or the quiet ones never get fixed.
Challenges & limitations
You can't ship zero bugs. Every real product has them, so the job is finding, ranking, and fixing the ones that matter, not chasing perfection.
Severity and priority get confused. Teams argue over labels, and a cosmetic bug in a high-stakes spot gets waved off as trivial.
UX bugs are contested. Unlike a crash, a "bad experience" invites debate about whether it's a real defect or a feature, so they often get dropped.
