Side car file
From The Glossary of Digital Photography
An additional file, created by the computer, to store metadata for the original (usually raw) file. The suffix on the file is .xmp. This system is used to keep from altering the original raw file, since it often contains proprietary and undocumented data. Keeping raw files together with sidecar files prevents the loss of metadata. Some software automatically keeps them together, but any manual moving of files, outside of the software, must be done carefully. See also raw
