bug vs error vs issue vs defect
Use "bug" in everyday conversation, "error" when something specifically fails or throws, "issue" when talking about a ticket in a tracking tool (bug or not), and "defect" only in formal QA or testing contexts.
bug
The general, informal word developers use for anything that behaves incorrectly. This is the default word in everyday conversation.
"There's a bug in the checkout flow, users can't complete their purchase."
error
A specific failure the system actually shows or throws, like an exception, a stack trace, or a message on screen. More precise than "bug."
"The app throws an error every time I try to log in with an expired token."
issue
The neutral, catch-all word used in ticketing tools (GitHub Issues, Jira). An issue isn't necessarily a bug, it can also be a feature request or a question.
"I opened an issue on GitHub for the missing confirmation button."
defect
Formal QA language for a flaw that causes the software to not meet its requirements. You'll see this in test reports and formal engineering processes, rarely in casual conversation.
"QA logged three defects after yesterday's release."
Other comparisons
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