One commonly cited definition, from the early 20th century, describes it as " falsification entirely disproportionate to any discernible end in view" .
Popper's falsification criterion is a great way to identify pseudoscientific fields like astrology, which makes overly broad predictions that adapt to any observation.
We would regard this act of historical falsification as something far more shameful if familiarity with the ecclesiastical interpretation of history for thousands of years had not blunted our inclinations for uprightness in historicis.