An order management system (OMS) for brokers is the software behind a broker's trading app that receives every order, checks it against the client's money and limits, and sends it to the exchange. The checking part is often called the RMS, the risk management system. Clients never see the OMS. They see only the app.
Here is what the OMS does with each order. First, it receives the order from the stock trading app, the broker's website or a dealer's screen. Second, it runs checks before the trade. Does the client have enough money, or enough shares to sell? For futures and options, does the client have enough margin, the deposit that the exchange requires? Is the price within the exchange's limits for that day? Is the quantity too large? Third, it sends the order to the exchange's matching engine. Fourth, it receives the result, updates the client's positions and tells the app. Fifth, it passes each executed trade to the broker's back office for post-trade processing.
Consider a client in Raipur who places an order to buy 500 shares at ₹820 each. The order is worth ₹4,10,000. But she has only ₹3,00,000 in her trading account. The OMS rejects the order in a few milliseconds, and the app shows "Insufficient funds". She changes the order to 350 shares, worth ₹2,87,000. This time, the OMS approves it and sends it to the exchange.
The hard part is the scale. On a busy day, a large Indian broker's OMS may handle millions of orders. Many of them arrive in the first few minutes after the market opens at 9:15 a.m. Every check must finish in milliseconds, and the system must not stop during market hours.
The OMS also follows the results of clearing and settlement. At the end of each day, the clearing house tells the broker how much margin each client owes, and the OMS uses these figures for the next day's checks.
A wealth order management system does a similar job for wealth firms. There, an adviser places orders for many clients at once, in shares, bonds and mutual funds.