1 Introduction  
2 Fact Definition  
2.1 Fact Granularity  
2.2 Fact Error Type  
3 Evaluation Methods Before LLMs  
3.1 Reference-based Evaluators  
3.2 Reference-free Evaluators  
3.3 Datasets and Benchmarks  
4 Evaluation Methods After LLMs  
4.1 Direct Evaluation  
4.2 Pipeline Evaluation  
5 Conclusion and Future Direction