Nebulous: Vague, cloudy, hazy.  Lacking definition, form or limits.

Nebulous comes from the Latin word nebula meaning “mist, or cloud”. 

We can use nebulous to mean cloudy, or hazy.  When driving to work during a dense fog, the roads may have a nebulous look.

But, we can also use nebulous figuratively.  For example, Sometimes, to get out of commitments we may use nebulous reasons.  

Or, most of us have nebulous goals and plans floating around in our heads.   Our chances of hitting those goals increase exponentially when we transfer those ideas to paper.  Clearly defined, written goals beat nebulous goals every day.