“Referencing” is a drop-dead simple idea, actually:   a reference is “a tiny thing” that refers to something else in memory.   That thing which is referred-to may be big or small, and there may be just one reference to it or a great many.   But each reference is very small and cheap.   So, for example, if you have in-memory a list of “big records,” you can swap and manipulate and what-have-you those records just by playing around with lists (or arrays, or hashes) of references to them:   nothing actually “moves.”   This lets you build up arbitrarily-complex data structures very easily, and to work with them very efficiently.   (Want to sort the same list of records by three separate keys at once, all in-memory, keeping all three lists, without making duplicate copies of anything?   Feel Free.™)   It’s one of the hallmarks of Perl and one of the compelling reasons for using this language.