What is a phonetically similar segment?

Definition
	Phonetically similar segments are two or more sounds which share phonetic features and are frequently found as variants of a single phonological unit in a language.

Discussion
	Most phonetically similar segments are adjacent to each other in a phone chart, and differ only slightly in one or two articulatory features.

Examples
	Here is a table that gives examples of phonetically similar segments and the difference between the given segments.
	The phonetically similar segments … Differ in … [p] and [b] voicing. [p] and [f] place of articulation and manner of articulation. [l] and [r] manner of articulation. [p] and [t] place of articulation.