Image Files

These hold a filesystem, much like a partition. This is a weird concept, but if you think about it, if everything in macOS and Linux is represented as a file, including partitions, it makes sense that a file can hold all the data from a partition or device. Image files are usually created by literally copying the file that represents a partition or a disk. Image files can have partitions inside too, just like a hard drive.

You might be wondering why these are helpful. Often they're used for backups, but also for data recovery. You can recover data from a bad DVD, say, and save the data into a file. This is good, because often after doing a recovery, some of the data you got turns out to be corrupted, and it needs to be analysed with another tool. It's much easier to do this if you recover to a file.