An audit is an independent check of a set of records: does the book say what it claims to say, and do the entries hold up against the evidence behind them.
The word gives away where the idea came from. It descends from the Latin audire, to hear. In medieval England accounts were not handed over to be read — they were read out loud, in front of the people who had to check them, partly because many of them could not read at all. The auditor was, literally, the listener.
That tells you what verification is for. The first tool humans invented against a dishonest or careless record was not a better document. It was witnesses: more than one person in the room.
It has a hard limit that is easy to miss. An audit checks a book against itself and against the paperwork supplied to it. It cannot, on its own, make the book agree with the world — as Wirecard demonstrated in 2020, when years of balanced accounts turned out to rest on confirmation documents that the two named banks said were forgeries.