Execution
Execution is the broker turning your instruction into an actual trade at an actual price.
The round trip takes time, usually a fraction of a second, sometimes a second or more when the market is busy.
A refused order comes back with a reason, such as not enough money, invalid price or market closed. The reason matters more than the refusal.
Also called: fill
Related terms
A definition, not financial advice. Trading carries a risk of loss.