1. Of a person, to have little experience of either a particular situation or activity, or of life in general, especially the unpleasant aspects of life. They mistakenly think that things are more simple than they really are.
2. They are often surprised by what is common knowledge for other. English = (be) inexperienced, (be) naive, (be) innocent. Idiomatic English = (be) wide-eyed, (be) green.