Glossary of Terms - W

WAN(Wide Area Network)
Network with computers far apart, connected by telephone lines or radio waves.LAN (Local Area Network))

Warning Letter
The most serious FDA postaudit (after inspection) letter notifying a manufacturer of adverse finding and giving it 15 days to reply.

Water Hammer
A tremendous force produced by rapid interruption of linear flow of a non-compressible fluid. Most commonly occurs when fast acting valves are closed in a high flow liquid system.

Water Treatment
Water treatment, also referred to as water conditioning, can consist of adding or removing chemicals to change the properties of water. In water softening, for example, sodium ions are substituted for metallic ions that cause "hardness" thus reducing the scale-forming tendencies of water. Water purification on the other hand, always consists of removing undesirable impurities.

Waviness
The more widely spaced component of surface texture. Unless otherwise noted, waviness includes all irregularities whose spacing is greater than the roughness sampling length. Waviness may result from such factors as machine or work deflection, vibration, chatter, heat treatment or warping strains. Roughness may be considered as superimposed on a "wavy" surface.

Western Blot
A procedure in which a mixture of proteins is separated on a polyacrylamide gel and then transferred to a nylon membrane. The membrane may then be treated with reagents such as specific antibodies to locate a protein of interest.

Wetted Surface
The surface(s) of any valve or component that will be exposed to a fluid (liquid or gas) when in service.

WFI (Water For injection), U.S.P.
WFI is water purified by distillation or by reverse osmosis, it contains no added substance. WFI meets the purity requirements under Purified Water. Although not intended to be sterile, it meets a test for a limit of bacterial endotoxin. It must be produced, stored, and distributed under Sterile Water for Injection.

White Blood Cell
A blood cell containing no respiratory pigment. In vertebrates it may be a polymorphonuclear leukocyte, a lymphocyte or a monocyte.

Workstation
An open or enclosed work surface, usually with direct air supply.

Worst Case
The highest or lowest value of a given control parameter actually evaluated in a validation exercise.