Confidence votes 33. First of all you are probably a 'rent asking this and not every word in the dictionary a teen has a slang word for, so remember that and don't critcize them just because they are WAY cooler than the kids next door!
When Raw Disk Image type is not mentioned explicitly in this guide, we are referring to the Backup Disk Image. Another file format supported is ISO image. ISO images are used to store a copy of CD/DVD/Blue-ray disc in a file and stand apart from actual disk images.
A snapshot consists of files that are stored on a supported storage device. A Take Snapshot operation creates .vmdk, -delta.vmdk, .vmsd, and .vmsn files. By default, the first and all delta disks are stored with the base .vmdk file. The .vmsd and .vmsn files are stored in the virtual machine directory. Delta disk files. A .vmdk file to which the guest operating system can write. The delta disk represents the difference between the current state of the virtual disk and the state that existed at the time that the previous snapshot was taken.