Air travel often carries a level of tension even before a passenger reaches the airport.

From coordinating transportation and checking baggage requirements to navigating terminals and tracking boarding times, travelers juggle dozens of small tasks at once. Add long security lines, sudden gate changes, or unexpected delays, and the experience can quickly become exhausting. In the middle of all this, many travelers discover something puzzling on their boarding pass—a short, four-letter code they have never noticed before.

That code, “SSSS,” stands for Secondary Security Screening Selection. It is an indicator used by the Transportation Security Administration to flag a passenger for additional screening before boarding. The presence of this code often surprises travelers because it is not announced in advance and usually becomes apparent only at the airport, when security procedures suddenly take longer than expected.