What do CTA and CTD mean?

CTA - no arrival possible

Once a "CTA" (closed to arrival) - closed for arrival, is set for a day, the guest can not book this day as a day of arrival. If he arrives before this day and remains beyond this day this is possible.

CTD - no departure possible

As soon as a "CTD" (closed to departure) - closed for departures, is set for one day, the guest can not book this day as a departure day. If he leaves before or later than this day, this is possible.