naive

Short definition from Wiktionary

Adjective

1. 1
   Lacking worldly experience, wisdom, or judgement; unsophisticated.
2. 2
   Not having been exposed to something.
3. 3
   Produced in a simple, childlike style, deliberately rejecting sophisticated techniques.
4. 4
   Intuitive; designed to follow the way ordinary people approach a problem.

Noun

1. 1
   A naive person; a greenhorn.