Orphan sections are sections present in the input files which are not explicitly placed into the output file by the linker script. The linker will still copy these sections into the output file, but it has to guess as to where they should be placed. The linker uses a simple heuristic to do this. It attempts to place orphan sections after non-orphan sections of the same attribute, such as code vs data, loadable vs non-loadable, etc. If there is not enough room to do this then it places at the end of the file.
For ELF targets, the attribute of the section includes section type as well as section flag.
If an orphaned section's name is representable as a C identifier then the linker will automatically see PROVIDE two symbols: __start_SECNAME and __end_SECNAME, where SECNAME is the name of the section. These indicate the start address and end address of the orphaned section respectively. Note: most section names are not representable as C identifiers because they contain a `.' character.