Okay kiddo, imagine you have a favourite toy that you like to share with your friends. But sometimes, you don't want to share as much and you only want to give a few toys to your friends.
Well, countries sometimes feel the same way about their products. They might want to sell lots of things to other countries, but sometimes they are worried that they might sell TOO much and hurt their own businesses. So they might decide to put a special agreement in place with another country to limit how many things they can sell to that country.
This agreement is called a "voluntary export restraint." It's like setting a rule for yourself so you don't get too carried away with sharing your toys. And just like how you might negotiate with your friends to limit how many toys you give them, countries can also negotiate with each other to agree on how many products they can sell to each other.
So basically, a voluntary export restraint is a rule that countries set for themselves to limit how much they export to another country so they don't hurt their own economy.