Commission is a fee a broker, exchange, or intermediary charges for executing an order. You may pay it when you buy or sell instruments such as shares, forex, commodities, futures, options, or CFDs.
Commission comes in a few forms: a flat fee per trade, a percentage of the trade value, or a charge that scales with volume. Some brokers bill it separately from the spread, while others fold most trading costs into the bid-ask spread instead.
Commission is a charge stated on top of the trade; the spread is the cost built into the gap between the bid and the ask price. Both feed total trading cost, so frequent traders, scalpers, and high-volume traders track commission closely, since small per-trade fees add up across many trades.
A broker charges USD 5 commission per share trade. You buy shares and later sell them.
You pay USD 5 to open the trade and USD 5 to close it.
USD 5 + USD 5 = USD 10
Total commission on the round trip is USD 10.