A "major breakthrough" refers to a significant advancement or discovery that dramatically changes the understanding or approach to a particular field. This can occur in various areas such as science, technology, medicine, or social issues. Breakthroughs often lead to new solutions, improved methods, or innovative products that can have widespread impacts. For example, the development of the COVID-19 vaccine represented a major breakthrough in public health, allowing for effective prevention of the virus. Similarly, advancements in artificial intelligence have transformed industries by enhancing efficiency and creating new opportunities for innovation.