The us.bin naming convention is common in older or Chinese-origin UEFI/BIOS updates. It is often a raw binary dump of the flash ROM. Unlike standard .ROM or .CAP files, .bin files are direct images that can be written via USB flashing tools, EEPROM programmers, or recovery modes.
The Basic Input/Output System (BIOS) is firmware that controls and configures the hardware components of a computer. Updating the BIOS can improve system stability, fix bugs, and add new features.