Definitions for "hairline"
Keywords:  thinnest, serif, bisque, gap, width
The thinnest possible line that can be drawn on a device.
Subjective term referring to very thin line or gap about the width of a hair: 1/100 inch.
The narrowest stroke in a font, except for the serif, or the thinnest that can be displayed on a printed page. A fine line dividing columns of type, marking the end of a block of copy, or outlining a page border. Also, a very thin typographic rule. The size of a hairline varies with the hardware and software used. Because the contrast between ink and paper affects visibility, there is no agreement on the meaning of hairline. The Graphics Arts Technical Foundation (GATF) defines it as a ruled line of 0.003 inch width, whereas the U.S. Postal Service describes it as a line of 1/2-point width (approximately 0.007 inch). Hairline is also used in reference to a very thin gap about the width of a hair 1/100 inch. See also FONT POINT RULE SERIF STROKE
the natural margin formed by hair on the head, especially the edge of growth of hair on the forehead; as, a receding hairline.
Receding part of male writer's body.
Keywords:  finest, rule, point, printers, standard
Finest standard printers rule.
A .5-point rule.
A .25-point rule.