Almost every retail order is held. You press buy, and the obligation is immediate handling under best-execution duties, not clever working of the order.
Held handling is right for small size, where waiting costs more in risk than it saves in price. It is wrong for institutional size, which is why not-held-orders and algorithmic-orders exist.
Example: a 300-share market-order in a liquid name is held and prints in under a second, inside the nbbo. The same instruction on 300,000 shares would be handled as not held, or broken into child-orders by a vwap-algo over several hours.
Related: not-held-order, market-order