A friend not long ago complained about the worst flight he had ever taken.
He was flying from Kansas City, our home base, to Phoenix. He said he had booked a “direct” flight but to his surprise, the plane made a stop in Salt Lake City. He was not expecting that and the flight took longer than he had anticipated.
I suspect my friend is not the only person confused by some airline terminology. There is a vast difference between “direct” flights and “nonstop” flights. And then there are “connecting” flights.

Direct:

While a direct flight might sound like its going to be a nonstop flight, it’s not. A direct flight makes at least one intermediate stop along the way to its final destination to let some passengers off and take on more.

Nonstop:

A nonstop flight is exactly what the name implies: a single flight between two airports with no stops in between. Business travelers prefer nonstop flights because they cut down on travel time, but they typically are more expensive.

Connecting:

To muddy the waters a little more consider another variation of air travel, connecting flights. That is where you start your journey on one plane that takes you to a central hub where you board a “connecting” flight that goes to your final destination. This is often called the hub-and-spoke system.

The hub-and-spoke system became the norm for most major airlines after the U.S. federal government deregulated the airlines in 1978.

The connecting flight is probably the most widely used system for managing travel. I primarily fly on Delta and it would be unusual for me not to fly through Atlanta or Minneapolis before getting to my final destination.

If you book your travel directly through the airline’s website you’ll see they are pretty transparent about the flights that are not nonstop. In the listing they’ll often indicate one-stop or two-stop and sometimes even list the names of the cities where you will be stopping.
Another clue is the length of the flight. If it seems it will take a long time between point A and point B look closely. Chances are you are booking a “direct” flight with stops along the way.