A nudge, as we will use the term, is any aspect of the choice architecture that alters people´s behavior in a predictable way without fordibbing any options or significantly changing their economic incentives. To count as a mere nudge, the intervention must be easy and cheap to avoid. Nudges are not mandates. Putting the fruit at eye level counts as a nudge. Banning junk food does not.
- from Nudge by Thaler and Sunstein