I've called the state of unset variables "nihil"... this is the isotopic state of void. I don't know if it's the best name but I definitely know I don't like calling it "unset" (I always say "variables are unset, not values").
The meta state of void is just a single apostrophe. Evaluating it produces void:
>> '
; void
The quasi state of void is a single tilde, and it evaluates to nihil:
>> ~
== ~ ; isotope <-- a.k.a. nihil
I mentioned that I prefer this to be the default for making an ARRAY if you don't specify an /INITIAL value because it is the reified stand-in for uninitialized-ness. Unlike blanks, it would error if you try to SPREAD it:
>> block: array 10
== [~ ~ ~ ~ ~ ~ ~ ~ ~ ~]
>> spread block.2
** Error...
This seems to me a better default than blank for any slots that you miss filling in for your arrays.
So what do we call ['] and [~]? Metavoid and Quasivoid? Tick and tilde? Is tilde a Metanihil?
I've also wondered if there's any better name for nihil.