.iso — Disc Image
Archive application/x-iso9660-image
What a .iso file is
A byte-for-byte image of an optical disc or an installer volume.
How to open it
Windows and macOS mount ISOs natively. To make bootable media, write it with Rufus, balenaEtcher or dd.
Worth knowing
Always verify the published SHA-256 of an OS image before writing it — hash it here.