RAW
An unprocessed camera sensor format retaining the maximum original image data, before any raster export decisions are applied.
In practice
A RAW file holds what a camera's sensor recorded, with little or no processing: with no white balance, sharpening or JPEG compression baked in yet. That leaves wide room to correct exposure and color later without visible damage. A product photographer shooting a white sneaker in RAW can recover detail in bright leather that a camera-made JPEG would already have lost. RAW files must later be developed and exported to an ordinary raster format for use.
Often confused with Raster
A RAW file is unprocessed sensor data from a camera; a raster is any pixel image, including the finished JPEG or PNG developed from that RAW.
Try this
If your phone or camera offers RAW, shoot one bright scene in RAW and JPEG, then try recovering the sky in each.