Commission

A commission is the fee a broker charges for executing a trade, historically a flat or per-share charge on every buy and sell order. US retail stock trading commissions largely went to zero starting in 2019, as brokers shifted to earning revenue through payment for order flow and interest on client cash instead.

The disappearance of visible commissions does not mean trading became free of cost entirely; execution quality (the actual price you get filled at) still varies by broker, and that hidden cost can matter more than a commission ever did for active traders.