Commission or Salary

What is the difference in Commission and Salary?

We are member of stock exchange and providing arbitrage platforms. A persons comes to our office, uses our infrastructure and funds and doing arbitrage activities,  and from the profits he gained, he is entitled for a sum determined on a fixed percentage. For example, If he gains Rs. 100 from arbitrage and the sharing ratio is 50%, then we will pay him Rs. 50.

What is the nature of this transaction? Whether is it a salary or a commission?