You make your airline reservation, get to the airport, check in, and get your boarding pass.

And then, you see it in four bold letters on that pass — SSSS.

What does that mean?

It stands for “Secondary Security Screening Selection.”

And that means you’ll be taken out of the normal security lane when you get to a checkpoint and given additional inspection.

So how did those letters get on your pass?

Immediately after 9/11, if anyone paid cash for their ticket, SSSS automatically applied.

Today, no one pays cash, but if you made your reservation within 24 hours of your flight time and you bought a one-way ticket, you fit the profile.