Global Entry is a trusted-traveler program of the United States government. If you have a “Known Traveler” number from Global Entry, you can bypass the long passport lines that travelers face when returning from international travel. The U.S. is not the only nation with this type of program, and this blog post describes the comparable programs that other countries have.
As you read the blog post, you will realize that the U.S. Global Entry program is much less expensive ($20/year) than most others.
You need to schedule and attend an in-person interview to get Global Entry. Most major U.S. airports have enrollment centers, and a new temporary one is opening soon in London.
I have had Global Entry for several years, and I highly recommend it. GE not only lets you re-enter the U.S. quickly, but it also gives PreCheck which gets you through domestic airport security without the nuisance conditions (shoes off, laptops out, liquids out) that other flyers face.