It's a situation that can have more than one interpretation, ^^

ambi = two The situation can be taken to mean two different things, so it is unclear.

An example of an ambiguous situation would be that of a person employed on a contract who didn't know whether he/she would have a job after the holidays.

Or sometimes specifically due to some grammatical error/flaw/lack/inadequacy, which is rather interesting to study and even hard to find a rephrase in the language to make what the speaker intends to express clearer: http://www.google.com/#hl=en&sugexp=ldymls&xhr=t&q=ambiguous+sentences&cp=11&pf=p&sclient=psy&aq=0&aqi=&aql=&oq=ambiguous+s&pbx=1&fp=3f8c1f6954acb9e1

Неопределенная, неясная ситуация. "Ambiguous" - Not clearly stated or defined