Definition: An absolute phrase (nominative absolute) is generally made up of a noun or pronoun with a participial phrase. It modifies the whole sentence, not a single noun, which makes it different from a participial phrase.Absolute phrases:
Its branches covered in icicles, the tall oak stood in our yard.
The tall oak, its branches covered in icicles, stood in our yard.
The tall oak stood in our yard, its branches covered in icicles.
As the main clause:
Its branches were covered in icicles.
Absolute phrases are always set off from the rest of the sentence by commas.
Sometimes when the participle of an absolute phrase is a form of the verb to be, the participle is left out and understood.
The movie being over, the patrons flooded the lobby and parking lot.
The movie over, the patrons flooded the lobby and parking lot.
Sometimes a noun phrase (a noun and its modifiers) can act as an absolute phrase.
The stars of that movie, where are they now?