An absolute allows us to move from a description of a whole person, place, or thing to one aspect or part. (See Martha J. Kolln's "Two Styles of Absolute Phrases" in Examples and Observations, below.)
Note that in traditional grammar, absolutes (or nominative absolutes) are often more narrowly defined as "noun phrases . . . combined with participles" (Macmillan Teach Yourself Grammar and Style in Twenty Four Hours, 2000). The term absolute (borrowed from Latin grammar) is rarely used by contemporary linguists.