Project Jigsaw is a major feature introduced in Java 9 that aims to modularize the JDK (Java Development Kit). It allows developers to break down the JDK into smaller, more manageable modules, making it easier to develop, deploy, and maintain Java applications. This modularization brings benefits such as improved security, performance, and scalability, as well as enabling developers to create custom runtime configurations tailored to their specific application needs. By modularizing the JDK, Java becomes more flexible and adaptable, allowing developers to only include the modules they need, reducing the overall footprint of their applications.