Core terms
Time in force (TIF)
The instruction for how long an order stays active, such as DAY, GTC (good till cancelled), IOC (immediate or cancel) or FOK (fill or kill).
A DAY order expires at the end of the session if it has not filled. GTC stays open across days, usually up to a broker-set limit. IOC fills whatever it can immediately and cancels the rest. FOK must fill completely and immediately or not at all.
Whether an order works in premarket or after hours is often a separate setting. A DAY order may not be eligible for extended hours unless you choose an extended-hours option.
What traders should verify
Check the TIF on every hotkey and order template. A forgotten GTC order can fill days later after news.
Do not conflate
Names and extended-hours behavior vary by broker and platform.