References in PHP are a means to access the same
variable content by different names. They are not like C
pointers, they are symbol table aliases. Note that in PHP,
variable name and variable content are different, so the
same content can have different names. The most close
analogy is with Unix filenames and files - variable names
are directory entries, while variable contents is the file
itself. References can be thought of as hardlinking in Unix
filesystem.