A mystery; something unpredictable.
a variable.
A symbol that resembles a variable or parameter but is used purely formally and neither signifies nor is ever assigned a particular value;
Not definitively or precisely determined, because of the presence of infinity or zero symbols used in any of several improper combinations.
With no genetically defined end, and thus theoretically limitless.
Designed to allow the incorporation of future changes whose nature is not yet known.
Not topped with some form of terminal bud.
Intersex.
Not accurately determined or determinable.
Imprecise or vague.