"True prophecy" refers to a prediction or foresight that is completely accurate and comes to pass exactly as it was predicted. It means that the prophecy is genuine and reliable, without any errors or inaccuracies in its predictions. Full definition
Now we are aware that frequently the authors and always the editors of the sacred writings were communities which in obedience and by inspiration selected true prophecy from false, genuine gospels from spurious ones, apostolic letters from epistles written by men who had no divine commission. (religion-online.org)