form-T, Nasdaq can now transact "after-hours" trades. These are trades that take place after the regular market close at 4:00 p.m. ET up until 6:30 p.m. ET. There is also a "premarket window" permitting Nasdaq trades before the regular trading session begins at 9:30 a.m. ET. These trades can take place as early as 8.00 a.m. ET.
Trades outside of regular trading hours are classified as "Form-T" trades. Form-T trades don't impact last, high, low or closing prices, but are reckoned in volume reporting. Nasdaq has specified that the "closing quote" of the regular session will be identified separately from extended-trading-hours quotes.