Learner's definition of NONRESTRICTIVE
not limiting or controlling something
It's a nonrestrictive diet that stresses eating smaller portions rather than not eating certain foods.
You'll be moving around a lot, so wear nonrestrictive clothing. [=clothes that do not make it difficult to move freely]
grammar, of a word or group of words
describing or giving more information about a person or thing but not needed to understand which person or thing is meant
In the sentence “My brother, who works at a restaurant, just got his first car,” “who works at a restaurant” is a nonrestrictive clause.