Sounds like part of a job or salary bonus offer. It means that the salary and benefits they offer will depend on merit - i.e. how much experience you have, how well qualified you are, or how well you have performed. It means that there is no set amount, it will vary from person to person.
When a student applies for a scholarship to attend college, he may qualify either for a merit-based or need-based scholarship. Merit-based would be based on your grades, SAT/ACT and extracurricular activities whereas need-based would depend on your financial situation.
So if a scholarship is purely merit-based, it means they don't care how rich or