Each bar is one departure, drawn from the moment passengers turn up until boarding closes. Where bars stack, the terminal is full.
Passenger numbers are an estimate, not a headcount. The default of 180 per flight is a full narrowbody. Nobody meeting or dropping off is counted, and staff are not either, so treat the curve as a shape rather than a number. Times are shown in the airport's own timezone. Data refreshes every 5 minutes.