What's the raw dictionary in Image I/O?

The Image I/O framework on iOS uses dictionaries to store image metadata.

One of these dictionaries is called kCGImagePropertyRawDictionary. The documentation says:

A dictionary of key-value pairs for an image that contains minimally processed, or raw, data.

What does this mean? What processing is being skipped when we access this dictionary that is being done when we access, say, the EXIF dictionary?