A neighboring tone is used to embellish
or emphasize a single tone. It may appear above or below the main tone and can be diatonic
(so long as chromaticism doesn't break your counterpoint
When dealing with chromatics, it is important to remember in your composition
that a chromtic leading tone is more colorful than a diatonic one and tends to draw more focus to the tone it is embellishing.
It is also possible to form a sort of pseudo-leading tone to whatever you want to emphasize
my placing the neighboring tone below the main tone.