indeterminate

Not accurately determined or determinable.

Imprecise or vague.

(mathematical analysis, of certain forms of limit) Not definitively or precisely determined, because of the presence of infinity or zero symbols used in any of several improper combinations.

(biology, of growth) With no genetically defined end, and thus theoretically limitless.

(botany, of inflorescences) Not topped with some form of terminal bud.

Intersex.

(architecture) Designed to allow the incorporation of future changes whose nature is not yet known.