This week Boston Logan Airport had a Ground Stop issued, and with the network outages across America, some airlines had them too. What is one?
A ground stop is a ban of all aircraft taking off or landing at an airport.
This could be due to a variety of reasons, but is primarily for safety - weather could be an issue (e.g. thunderstorms), or there could be a security alert on the ground, or concern about something that may be on board a plane.
It's usually issued by the FAA, but could be issued by an individual airport as well.
Flights already inbound may be directed to other cities to land there instead.