In traditional finance, a limit order is an order to buy or sell a security at a specified price. When you are buying, you instruct your broker not to go higher than the specified price. And when you are selling you instruct broker not to sell below your specified price.
At KyberSwap, a limit order is an order to swap tokens at a specified rate. For example : A user wants to swap WBTC token to DAI token only if rate reaches 15,000 (assume current rate is 11,000). KyberSwap will execute the swap order only if rate >= (15,000).
The advantage of placing a limit order is that you can place buy/sell order at your desired rate. However, there is a chance that your order may not get filled as your desired rate may never be reached.