Factuality is the property of a model output being consistent with reality or established facts. It is especially important for question answering and information tasks, although creative tasks may appropriately prioritize imagination over factual accuracy.
Within the ML world, a property describing a model whose output is based on reality. Factuality is a concept rather than a metric. For example, suppose you send the following prompt to a large language model: What is the chemical formula for table salt? A model optimizing factuality would respond: NaCl It is tempting to assume that all models should be based on factuality. However, some prompts, such as the following, should cause a generative AI model to optimize creativity rather than factuality. Tell me a limerick about an astronaut and a caterpillar. It is unlikely that the resulting limerick would be based on reality. Contrast with groundedness.