"Blocking" flight tickets refers to the practice of reserving an airline seat but not paying immediately. This is usually done by travel agents or by representatives booking travel for a group of 10 or more people, but in a few cases, you can get the same effect – if within a shorter time frame – as an individual doing your own bookings.
The 24-Hour Rule
If all you need is a little more time to think about your booking, the U.S. Department of Transportation's "24-Hour Rule" is on your side. It states that as long as you book your flight at least seven days in advance, the airline must allow you to either hold the reservation for 24 hours without penalty, or to cancel (within that 24-hour time period) without penalty. You can usually do this straight through the airline's online booking system or with their customer service agents, but make sure you read the fine print. Some airlines require you to pay immediately but offer the penalty-free cancellation for 24 hours, while others give you the choice between holding your ticket for 24 hours without payment.
If you need to pay for an airline ticket in person – for example, if you're using cash or a voucher that must be redeemed at the airline counter – the 24-hour hold gives you time to make that transaction.
Holding Individual Tickets
If you're traveling on your own or in a small group, there are two ways of blocking a flight beyond that 24-hour time period. Option number one is to contact the airline directly and ask for a temporary block, which you'll receive – or not – at the discretion of the airline. Airlines that offer this service usually hold your seat for about 72 hours and may charge a small fee for the service. Or, you can go through a third party like Clear Trip or Yatra that temporarily holds a seat for you, giving you more time to pay or arrange your other travel plans. Often, these third-party services act as consolidators that buy blocks of seats from airlines at a very steep discount, then resell the seats to individuals at a lesser discount.
Blocking Flights for Large Groups
Some airlines will let you block seats for large groups of people – usually 10 or more. To do this, you'll need to contact the airline directly. If you represent an official group – say, a sports team or a business corporation that regularly flies large groups back and forth – you may have a designated representative at the airline that can help you. If you're a private individual booking tickets for something like a destination wedding, it's a toss-up whether the airline will deal with you directly. If they won't, you'll have to go through a travel agent.
Whether you're blocking tickets for yourself or a large group, always do this sort of booking well in advance. Airlines usually won't allow blocked tickets for travel that's coming up soon, and, in fact, the U.S. Department of Transportation's mandatory 24-hour hold rule doesn't apply to flights booked less than seven days before travel.
Confirm the Terms
Confirm the terms of your blocked tickets with the airline or your travel agent; get the terms in writing if at all possible. Make sure you know how long you have to pay for the seats and what will happen to any seats that aren't paid for. You might lose them entirely, or you might have the option of "buying them back" at a higher rate.