When you use a digital camera, you may have the option to save the photo you've taken as a raw+JPEG file. This is a quasi-standardized file format that bundles a JPEG with the unmodified sensor information that forms a raw file. The benefit of using raw+JPEG include the ability to quickly preview the file anywhere, while also still having access to the underlying data for carving out a version of the photo.
A lot of software (including Apple Photos) now supports importing and reading popular raw formats, so you can bypass changes imposed by cameras and photo apps for further editing without losing the original detail.
Reader Luke Hartman has imported raw+JPEG files, and has a question about managing those files.