Welcome to FT, Summer.

If the SSSS designation appears on your boarding pass, that means that you have been selected for an additional thorough screening. They will pull you aside and wand you, pat you down, run the explosives detector patch on your shoes and carryons, and then go thru the carryons looking over your items piece by piece.

This is a giant pain in the a$$ and there are some things that you can do to minimize your chances of getting it. Altho it is frequently randomly given out, we think that actions like buying a one-way ticket, buying a ticket with cash, or changing your frequent flyer number when you check in (or maybe even at any time after you buy your ticket) may trigger the algorithm.

Also, try to check in online. If you have done everything correctly and there has been no substantial schedule change in your flight, a turndown with no boarding pass being issued to you frequently means that you have been selected and the BP that you get at the airport will have the SSSS. When that happens, you know that you need get there early leaving a little extra time for the search.

What the geniuses in Washington don't seem to realize is that they have made the whole thing virtually useless since any aspiring terrorist who can't get his BP online can merely scratch that trip and try again on another.