Android Custom ROMs are modified versions of the standard Android operating system. They are created by developers to enhance features, improve performance, or provide a different user experience. Users can install these ROMs on their devices to access new functionalities that may not be available in the official version. These custom ROMs often come with additional customization options, improved battery life, and updated security features. Popular examples include LineageOS and Pixel Experience. Installing a custom ROM typically requires unlocking the device's bootloader and using a custom recovery tool, which can void warranties and may carry risks if not done correctly.