TSA PreCheck is a program run by the Transportation Security Administration (TSA) that allows pre-approved travelers to undergo expedited security screening at airports. When you have Precheck, you'll typically be ushered into a separate (sometimes shorter) line than standard security. Besides enjoying a shorter line, Precheck passengers also get to keep their shoes on, their appropriately sized liquids in their bags, and their laptops in their bags, too.
There are some stipulations. TSA agents can, for any reason, ask you to remove your shoes, liquids, and laptops if they deem it necessary. And sometimes, TSA Precheck security lines have different hours than the regular security lines. Also, you can't use TSA Precheck on every airline, though many participate in the program.
Too use TSA Precheck, you must enter your Known Traveler Number (KTN) into your flight reservation—it can be done online via your airline's website or app, or at the check-in desk at the airport.
TSA Precheck costs $78 for a five-year membership, after which you can renew at $70 per year. (Many credit cards will reimburse you for TSA Precheck as a benefit.) A bonus: TSA Precheck members can bring with them children under 12 without paying for extra memberships.