What is "twip"

n. (context computing English) A unit of measure equal to one twentieth of a point.

A twip (abbreviating "twentieth of a point", "twentieth of an inch point",The Free On-line Dictionary of Computing:

http://foldoc.org/twip or "twentieth of an Imperial point" ) is a typographical measurement, defined as 1/20 of a typographical point. One twip is 1/1440 inch or 17.639 µm when derived from the PostScript point at 72 to the inch, and 1/1445.4 inch or 17.573 µm based on the printer's point at 72.27 to the inch.