- The definition of foolproof is something that is designed or set up so it would be difficult or impossible to make a mistake or an error during use.
When an appliance is designed with very-simple to use buttons that even a really dumb person can use, this is an example of a time when the appliance is designed to be foolproof.
- Designed so as to be impervious to human incompetence, error, or misuse: a foolproof detonator; a foolproof safety lock.
- Effective; infallible: a foolproof scheme.
(comparative more foolproof, superlative most foolproof)