Fill
A confirmed execution of an order — the trade happened, shares changed hands at a specific price and time.
A fill is the completion of an order. When your order executes, you receive a fill report confirming the quantity traded, the execution price, and the timestamp. Multiple partial fills at different prices can satisfy a single order.
The average fill price is the volume-weighted average of all partial fills, and this is the price that determines your cost basis or exit proceeds.
Tracking fill quality — comparing your fills to VWAP, the NBBO at time of order, and benchmark prices — is how institutions measure execution performance over time.
On the desk
Wanting 5 contracts and receiving 2 means your risk math changed. Recalculate or exit. Do not pretend you have the original trade.