What does invalid BSD file type mean when repairing a Mac disc?

The "invalid BSD file type" error when repairing a Mac disk typically indicates a corruption in the file system or an issue with the disk's partition structure. BSD (Berkeley Software Distribution) refers to the underlying file system used by macOS. This error can prevent the disk utility from properly accessing or repairing the disk, potentially requiring more advanced troubleshooting or data recovery methods if the disk is severely damaged. In some cases, reformatting the disk may be necessary, but this will erase all data.