The macOS Installer is a software application used to install or upgrade the operating system on Apple computers. It provides a user-friendly interface that guides users through the installation process, allowing them to set up their system preferences and choose installation options. The installer can be accessed from the Mac App Store or downloaded directly from the Apple website. Once the macOS Installer is launched, it verifies system compatibility and prepares the necessary files for installation. Users can choose to perform a clean installation or upgrade their existing system, ensuring that their data and applications are preserved. This tool is essential for maintaining the latest features and security updates on a Mac.