The results of test set and verification set differ greatly. What is the problem？

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Hello, I used your Quora data set and the corresponding configuration to train 10 EPOCHs on the model. During the whole training process, the ACC of the verification set performed well, about 87%. However, when I tested the test set with the trained model, the ACC decreased significantly, fluctuating between 52% and 58%, which made me very perplexed.
May I ask what the reason is?