Participle clauses are a type of ____

A participle is a form of a verb - either ING or Past Participle (3rd form of a verb). A participle clause is a subordinate clause which begins with a participle. They act like adverbs and are linked to the main clause of a sentence. They usually show things like event order, time, cause and effect:

Example: Stepping on camera, I relaxed completely. (When I stepped on camera)

Source: engvid.com & Cambridge Dictionary Grammar reference.