o·pen-end·ed (pn-ndd) adj.

1. Not restrained by definite limits, restrictions, or structure.

2. Allowing for or adaptable to change.

3. Inconclusive or indefinite: “faintly bemused and uneasily open-ended about the whole horrible business” (Charles Michener).

4. Allowing for a spontaneous, unstructured response: an open-ended question.

http://www.thefreedictionary.com/open-ended

 

Definition of OPEN-ENDED

: not rigorously fixed: as
a : adaptable to the developing needs of a situation
b : permitting or designed to permit spontaneous and unguided responses