A good feature has which of the following characteristics?

A good feature is indeed characterized by the requirement that it should be known at prediction time and relate to the objective. This means that when you make predictions or classifications, the features used must be available to the model at that moment, ensuring the model can operate effectively in real-world scenarios. Additionally, relevant features should have a meaningful relationship with the target variable, which helps in making accurate predictions.

Features that fulfill these criteria are essential for model performance because they contribute to the model's ability to generalize and make accurate predictions in unseen data. Known features that are closely tied to what you are trying to predict improve the model's reliability and robustness.

This characteristic also highlights the importance of careful feature selection in machine learning, as irrelevant or unmeasurable features at prediction time can degrade model performance.