Adjuncts include adverbs and adverb phrases, clauses of various types, prepositional phrases, and other kinds of phrases: they serve as qualifiers and modifiers to the core of a sentence, and hence can sometimes be moved around the sentence to various optional positions.
Adjuncts can be classified by how they relate to the rest of the sentence:
adjuncts of manner: Whisper ran quickly (ADV); Whisper ran very quickly (ADV P); Whisper ran in a big hurry (PP); Whisper ran, his feet flying (-ing clause); Whisper ran, taking a shortcut across the lawn (-ing clause)
adjuncts of location: In the yard, Whisper plays with Gemma (PP); Whisper sleeps on the couch (PP)
adjuncts of time: I saw Whisper yesterday (N); Whisper will appear any minute now (NP); Whisper will arrive in a minute (PP); Whisper played with Gemma for fifteen minutes (PP)
adjuncts of degree: Whisper plays a lot (NP); Whisper plays often (ADV); Whisper plays on rare occasions (PP)
adjuncts of cause: Whisper ran to catch the mouse (infinitive clause); Whisper is limping due to a fight with a possum (PP with two-word P "due to")
adjuncts of domain: Generally, Whisper is a good cat (ADV); When it comes to mice, Whisper is a killer (wh- clause); From the perspective of hunting, you can't fault Whisper (PP)