Phase IV refers to the final stage of clinical trials for new drugs or treatments, where the product is monitored for long-term effects and effectiveness after it has been approved for public use. This phase helps identify any rare side effects or long-term health impacts that may not have been evident in earlier trials. During Phase IV, researchers collect data from a larger population, often through post-marketing surveillance. This ongoing assessment ensures that the benefits of the drug, such as vaccines or medications, continue to outweigh any risks, contributing to public health safety and informed medical practices.