General synonyms:
* Vagueness
* Unclearness
* Obscurity
* Indeterminacy
* Doubtfulness
* Uncertainty
* Openness to interpretation
* Double meaning
* Open-endedness
More specific synonyms:
* For something unclear or confusing: confusion, bewilderment, perplexity
* For something with multiple meanings: equivocation, double entendre, polysemy
* For something open to interpretation: open-endedness, suggestiveness, suggestibility
The best synonym to use will depend on the context of your writing.