term:

Vague

vague adj

: characterized by such a lack of precision that a person of ordinary intelligence would have to guess if particular conduct is being proscribed
: characterized by a failure to describe forbidden conduct in terms sufficient to provide fair warning [an unconstitutionally law] see also void-for-vagueness doctrine compare overbroad
vague·ly adv

vague·ness n

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.