What is difference between ActiveReservationa and WaitingReservation, can we use RabbitMQ

Does ActiveResService mean that it loads the already booked tickets ?

Does WaitingReservation mean people who are currently blocked the seats.

Can we use RabbitMQ or some message queues for the above services instead of HashMap ?

In one of the interviews I was asked a question about Designing Flight Runway where In a minute a certain flights could be landed, if limit exceeds we should not allow other flights ?

I asnwered about using HashMap and the interviewer was not convinced.

I agree, a message queue is a great option, I was asked about designing a bank account with a number of users deposit / withdraw, he suggest use message queue.