Artifact

An artifact is an unintended and undesirable by-product of a process or treatment which has been applied to an audio track in excess. Artifacts are NOT inherent in the source material; they are created or induced by a process, and in many cases are irreparable.

Artifacting can occur regardless of the plug-in or brand of device being used. Artifacts are typically induced during restoration processing, but can result from any process, no matter how benign.

Some common processes and their artifacts:

The Process: Broadband Noise Reduction - the desired result is to reduce various forms of noise in a track such as optical film noise, tape hiss, production noise, etc.
The Artifact: a metallic sounding, swishy phasing.

The Process: De-Clicking/De-Crackling - the desired result is to remove transient anomalies such as ticks and pops.
The Artifact: a very low frequency thumping.

The Process: Dynamic Compression/Limiting - the desired result is to make the quietest portions of program louder and the loudest portions of program quieter.
The Artifact: a pumping, or severe and distracting rapid fluctuations in levels.