The Collaborative International Dictionary of English v.0.48:
Kern \Kern\, v. t. [imp. & p. p. Kerned; p. pr. & vb. n.
Kerning. ] (Type Founding)
To form with a kern. See 2d Kern.
The Free On-line Dictionary of Computing (18 March 2015):
In typography, the process of adjusting the spacing
between certain pairs of characters to improve the appearance of
the text. Roughly speaking, this can be thought of as equalising
the area of space between adjacent characters. Each character
of a proportional font has a width that includes some space on
either side so that adjacent letters don't touch. Some pairs of
characters such as A and V, look better if the spaces overlap
slightly, bringing the characters closer together (but still not
touching). In most cases, kerning reduces the spacing ("negative
kerning") but some pairs like "r" and "y" look better with extra
space ("positive kerning").
See also tracking, leading.