You get a background check from TSA. It is $85 for three years, worth every penny when you arrive home you walk past the whole customs line. No customs forms to fill out.
Refer to Len's previous post about the App vs. TSA pre-check vs. Global Entry. Pre-check is $85 and requires a background check by TSA, but only expedites security checkpoint within US. Global Entry is $100 and requires a background check by CBP (more thorough). This program expedites entry into US. It also qualifies you to use the TSA pre-check when travelling domestically.
Also, key to note... ALL the people in your traveling party must have whichever... if only one person has TSA/GE/pickyourpoison, then the other person still has to use the regular lines. Especially important to note for those that use the credit card, which will provide a reimbursement for ONE person.