Heatmaps are data visualization tools that display user data on a website through color density maps, providing insights into user behavior and traffic patterns. They help optimize websites for conversions by showing how users interact with the UI, identifying frequently clicked buttons and areas of interest. Different types of heatmaps include scroll maps, click maps, and session recordings, and popular heatmap tools include FullStory, Hotjar, Crazy Egg, SmartLook, and VWO Insights. Regularly testing and analyzing high-traffic pages can provide valuable insights to improve the user experience and lead visitors towards conversions.