Gram. in Latin, a grammatically independent phrase containing a noun in the ablative case and a participle, pronoun, or second noun also in the ablative case, used to express time, cause, or circumstance
See ablative absolute in American Heritage Dictionary 4
noun
In Latin grammar, an adverbial phrase syntactically independent from the rest of the sentence and containing a noun or pronoun plus an adjunct, usually a participle or adjective, with both elements in the ablative case.