Bug
A bug is an informal term for a defect — a flaw in code that causes incorrect or unexpected behavior. Most teams use "bug" and "defect" interchangeably in conversation, reserving "defect" for the formal record logged in a tracker. Either way, it's the same underlying problem: code doing something other than what it should.
The word comes from a (possibly apocryphal, definitely popular) story about a literal moth found in a Harvard Mark II relay in 1947 — but "bug" as a term for a fault predates that by decades, showing up in Edison's notebooks in the 1870s.
Whether a team calls it a bug or a defect rarely matters day to day. What matters is treating both the same way: every one gets a severity, a priority, a reproducible set of steps, and a place in the defect lifecycle from Open to Verified to Closed. Teams that use "bug" casually in stand-ups but "defect" formally in Jira are describing the same thing with two names — the distinction is tone, not process.
