Zip archive for the Xiaomi Mi4 smartphone, 1.34 MB in size. The name does not say what is inside, so it could hold schematics, a board layout or service notes rather than firmware. Small archives of this kind for phones usually contain PDF circuit diagrams or component placement drawings used to trace power rails, find test points and identify parts around the charging, display and PMIC circuits. Extract it and check the contents, then make sure the board revision printed on your phone PCB matches the documents before you rely on any measurement or part location.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @Schematics_Mobile. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.