defect

Defect is a term used as both noun and verb. As a noun, it denotes an imperfection or deviation from a standard, function, or expectation. It can refer to flaws in objects, systems, processes, or biological conditions. As a verb, to defect means to abandon allegiance or association with one group or country in favor of another; the noun defection is used for the act.

In manufacturing and engineering, a defect is a nonconformity that fails to meet specifications or requirements. Defects reduce performance, reliability, or safety. Quality-control systems track defects with terms such as defect rate or defect density, categorize defects by severity (minor, major, critical), and pursue corrective actions through root-cause analysis and process improvement. Product defects can arise from design flaws, material faults, manufacturing errors, or improper use.

In materials science and solid-state physics, defects are irregularities in a crystalline lattice that influence properties. Common types include point defects (missing atom vacancies, interstitials), substitutional defects, line defects such as dislocations, and planar defects like grain boundaries or stacking faults. Defects can alter mechanical strength, electrical conductivity, diffusion, and optical behavior.

In software engineering, a defect (or bug) is an incorrect or missing function that prevents software from performing as intended. Defect management includes reporting, triaging, reproduction, fixing, and verifying through testing to prevent recurrence.

In biology and medicine, a defect may denote a congenital or developmental abnormality, sometimes called a malformation or genetic defect, arising from mutations or environmental factors.

Defection, in politics and history, is the act of leaving one country, faction, or organization to join another.