Data that has not been processed for use. It is often written as ‘RAW’, which may make you think it is an acronym. It is not.
Raw data usually applies to the output of digital cinematography cameras that can generally deliver images that include the full brightness range that its imager can extract from a scene. The data has not been tampered with, not processed for color or to suit any target viewing conditions, such as cinema or gamma corrected for home TV viewing. The raw data is as the imager saw it with debayering applied where needed.