Thank you for creating this dummy item. It helped me!
Unlink refers to the underlying UNIX command, unlink, which removes the symbolic or hard link to the file, not necessarily the file itself. The file is only removed when all links to the file are removed.
A "dummy entry" is a "fake" entry or, in this case, an entry for a command that does not actually exist, so that people can find the correct one. The word "dummy" is used in the same way as in the expression "a tailor's dummy", which is a fake person used to stand in for a real client so that they can see the results of the work.
php is a C like language - the syntax is similar,
most of the functions in PHP are pulled from C standard libraries (and POSIX)
"unlink" is a C function. (originally POSIX, but recently standardised by ISO as _unlink)
"delete" is a CP/M command which is same as the "era" CP/M command
"del" is a MS-DOS command that is same as the "erase" MS-DOS command