Execution is everything between the click and the fill landing on the broker's books. Speed, routing, requoting, the price you actually got. The advertised spread is the headline. Execution is what shows up on the receipt.
FINRA Rule 5310 sets the floor for US brokers. They must use reasonable diligence to find the best market for an order and execute at the most favorable price available. They also have to review their execution quality on a regular basis, security by security and order type by order type.
Two brokers can quote the same spread and produce different outcomes because their execution differs. How they handle your order matters. Do they pass it straight through to liquidity, or internalize it? Do they requote in fast conditions? Do they accept partial fills? How fast does their server confirm? Each answer has a price tag.
Algorithms feel execution more than humans do. A few extra milliseconds between signal and fill shift the realized entry by a fraction of a pip. Times five hundred positions a month, that fraction is a real bill. A strategy that looked great on a fast broker can underwhelm on a slow one.
Javlot routes to partner brokers chosen on execution quality for the specific demands each strategy makes. Scalpers need different broker behavior than swing strategies. The performance you read on a strategy page came back from real fills on real partner brokers, not a clean lab number.