Terminology

The standard US terminology for Nondestructive testing is defined in standard ASTM E-1316.Some definitions may be different in European standard EN 1330.

Indication
The response or evidence from an examination, such as a blip on the screen of an instrument. Indications are classified as true or false. False indications are those caused by factors not related to the principles of the testing method or by improper implementation of the method, like film damage in radiography, electrical interference in ultrasonic testing etc. True indications are further classified as relevant and non relevant. Relevant indications are those caused by flaws. Non relevant indications are those caused by known features of the tested object, like gaps, threads, case hardening etc.

Interpretation
Determining if an indication is of a type to be investigated. For example, in electromagnetic testing, indications from metal loss are considered flaws because they should usually be investigated, but indications due to variations in the material properties may be harmless and nonrelevant.

Flaw
A type of discontinuity that must be investigated to see if it is rejectable. For example, porosity in a weld or metal loss.
Evaluation
Determining if a flaw is rejectable. For example, is porosity in a weld larger than acceptable by code.

Defect
A flaw that is rejectable — i.e. does not meet acceptance criteria. Defects are generally removed or repaired.
Penetrant testing
Non-destructive test typically comprising a penetrant, a method of excess removal and a developer to produce a visible indication of surface-breaking discontinuities.