Oracle VirtualBox is a free and open-source virtualization software that allows users to run multiple operating systems on a single computer. It enables users to create and manage virtual machines, which are isolated environments that can run different operating systems like Windows, Linux, or macOS without affecting the host system. With VirtualBox, users can easily switch between different operating systems, test software, or run applications that are not compatible with their primary OS. It supports various features such as snapshots, which allow users to save the state of a virtual machine, and shared folders for easy file transfer between the host and guest systems.