digital photography RAW files are the files that most cameras can output and allow to be saved on your memory card or computer which contain the raw digital data derived from the sensor with usually no image processing performed on the file but with added metadata stored within the file relating to the camera used, time, date, settings used (such as white balance, shutter, aperture, ISO) and in some cameras, GPS location data.

you cannot view the image of a RAW file without it first being processed by a RAW converter software.

unfortunately each camera manufacturer has its own proprietary formatting of the RAW file and this changes with each model they put out which usually means when you buy a new camera, you will need to update your RAW converter software (fortunately, when you buy the camera it usually comes with the manufacturer's version of RAW conversion software included to get you started).

RAW files tend to be quite large (10-20Mb is common for 10 mpixel cameras), although some manufacturers have smaller files due to lossless compression of the RAW files.

altering white balance is significantly easier and as it is in 12-14bit space rather than jpeg's 8 bit space gives better results.

RAW files hold more highlight data and thus allow errors in exposure to be more readily corrected as well has high contrast scenes better able to be post-processed. Thus blown highlights can be corrected more effectively although perhaps not completely.

as it holds all the RAW data, even better quality images may be obtainable in the future as RAW conversion software improves.

some manufacturers allow an alternative smaller RAW file which converts into a lower resolution image than the full RAW file (eg. Canon's “sRAW” file - although this is of dubious benefit but may be useful for action photographers who want to post-process their rapid burst images and are not so concerned with image resolution. 

as an attempt at creating a generic RAW file format which hopefully will be more likely to be accessible in the future, Adobe have created their RAW file format called DNG, so many users convert their original proprietary RAW files to DNG format.

each manufacturer tends to use their own file extension name for their RAW files:

Adobe: .dng - also can be created in camera by Pentax K10D, Leica M8, Hasselblad H2D, Samsung pro 815.

Olympus: .orf

Panasonic: .RW2

Canon: .crw

Nikon: .nef

introduced into Apple iPhones in 2017

HEIF or High Efficiency Image File Format is a more efficient image format than JPEG and is based upon “High Efficiency Video Compression” or H.265.

the format allows you to store twice the data as JPEG without increasing the file size and allows 16 bit not just 8 bit which is the case with JPEGs

manufacturer's proprietary software - often limited capabilities and of course only does the one format

third party RAW file processing software - see image editing software