An exclusive mandate means that one person or group is chosen to do something, and other people or groups are not allowed to do the same thing. Think of it like a game of tag - if your friend gives you the "exclusive mandate" to tag people, then you are the only one who can do it, and nobody else is allowed to tag people.
In business, an exclusive mandate is like a contract that says only one person or company can sell or do something. For example, a company might get an exclusive mandate to sell a certain product in a particular country, which means that nobody else can sell that product in that country except that company. This can be a good thing for the company because it gives them a competitive advantage and helps them make more money.
But sometimes exclusive mandates can be bad for competition and can limit the choices that people have. For example, if there's only one company that can sell a product, they might be able to charge higher prices because there's no competition. That's why some countries have laws to make sure that exclusive mandates don't hurt consumers.