What is a bug?

Error, bug, defect, failure and fault [swe]

tl;dr

An Error/Mistake in code generates a Defect/Bug, if the system does not perform as intended then it is a Fault, and if the user notices the fault, it is a Failure.

error/mistake -> defect/bug/fault -> failure

Differences

“When a developer commits a mistake in code it is called Error, when the error is found during tests it is called Defect, when a defect is sent to production then it is called Bug, when the system doesn't perform as intended due to lack of resources or invalid data then it is a Fault and when the user perceive the fault or bug/defect then it Is Failure”

Error

A mistake, misconception or misunderstanding from the developer (dev, sw, qa, etc) that leads to a bug/defect or a fault.

Bug/Defect

Variance between expected and actual. The requirement is: wrong, missing or extra.

Fault

Incorrect step, process or data definition that causes the program to perform unintended.
Ex: lack of resources or invalid data

Failure

Not perform functions within specified performance and/or requirements.

Issue

It means any activity in the software development cycle where
the source is some anomaly or flaw that need to be fixed. Ex: documentation, bug fix and requirement change.

Technical Debt

A technical debt is an action in the software development life cycle that was intentionally delayed (that can or cannot generate a bug later).