These are the image files for the mvebu/cortexa9 target.
Check that the md5sum of the file you downloaded matches the md5sum below.
Shortened image file names below have the same prefix: immortalwrt-18.06-snapshot-r8179-cab1e2e283-mvebu-cortexa9-...
These are supplementary resources for the mvebu/cortexa9 target. They include build tools, the imagebuilder, md5sum, GPG signature file, and other useful files.