adverb
An adverb is a word that describes or gives more information about a verb, adjective, or other adverb. In this case, 'ad fin' is an adverb that modifies the verb or adjective it is associated with.
The project was completed ad fin, with every detail meticulously executed.
I finally finished painting the house ad fin, it took forever!
I aced that exam ad fin, no doubt about it.
She pursued her dreams ad fin, never giving up despite the challenges.