The seat number you never want to see on your boarding pass – as you could miss your flight

YOUR boarding pass holds plenty of information, including where you're going to be sat on the plane.

But there's one number you definitely don't want to see next to your seat number - and that's zero.

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Most passengers are given a seat number once they've checked into their flight online.

This number can be anything from 1A to 33C, and everything in between, with most passengers hoping to avoid the dreaded middle seat like the plague.

Even though the middle seat might feel like the worst option, there's a seat number that's far more worrying.

This is the number zero, which means a passenger hasn't been allocated a seat during check-in.

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Travel Creator James Scoffin told Sun Travel: "They give you a seat allocation of 0 on your boarding pass, which means you have checked in, but not actually been given a seat."  

The seat number zero is often printed on boarding passes when a flight is very full and there are very few unassigned seats remaining.

One person explained an airline's decision-making on where they wrote: "It is easier to assign people a seat than to change a seat assignment. People get very upset if they get moved.

"Sometimes seats have to be reassigned very close to departure. For example, if a seat has recently become broken or unusable, adults with small children have not been seated together, an unsuitable passenger has been assigned an exit row, and similar.

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"It is much easier to keep a few seats unassigned and not assign a seat to the last few passengers to check-in."

While it's likely a seat will be assigned at the boarding gate, this isn't always guaranteed - especially if the flight is overbooked.

If a flight is overbooked, and a passenger hasn't been given a seat number, they could be bumped from that flight and be forced to wait for the next service.

Those passengers who aren't allocated a seat number should head to the airport armed with all the confirmation and booking references, just in case.

Another code you don't want to see on your boarding pass is SSSS, which stands for Secondary Security Screening Selection.

It means that the passenger has been selected for additional screening by security – where officials will give you a pat down, swab for explosive residue and open up all of your bags.

A lot of the time passengers are just picked at random, but if you find the code on your plane tickets regularly then the chances are you're being monitored by the US Department of Homeland Security.

A TSA source said that paying for tickets in cash or buying lots of one-way tickets could get you on the SSSS list.

Stewart Jackson, from London, received the dreaded "SSSS" letters stamped on his boarding pass when flying out to New York to visit his girlfriend.

While Stewart had to undergo an extra security search at his boarding gate, he wasn't delayed and didn't miss catching his flight.

There are other codes on your boarding pass too, for instance, the two letters at the start of the flight number denote the airline.

These two-letter codes are issued by the International Air Transport Association (IATA), the trade association for international airlines. And of course, no two airlines can have the same code.

Many seem like no-brainers. QF is Qantas, Virgin Atlantic is VS, AA is American Airlines, BA is British Airways and NZ is Air New Zealand.

The numbers reveal a lot more information. For starters, the lower the number, the more prestigious the route — such as Qantas’ Sydney-London service, QF1.

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Meanwhile, there are lots of codes on your boarding pass you need to know about too.

Here's why you should never take a photo of your boarding pass.

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