If you don't live in a rural area of the U.S., imagine driving along a country road and a vehicle (probably a pickup) approaches from the other direction.
If it's a gravel road, you definitely won't want to take either hand off the wheel to wave, because you'll risk losing control of your vehicle and going into the ditch.
Instead, when you and the other driver are close enough to see each other, you raise one finger.
Doesn't matter which finger, but the index finger is most common. The other driver does the same. Maybe you'll smile too, but this isn't a requirement.
And that's all there is to the One Finger Wave.
Drivers from rural areas being friendly.
City Slickers who aren't used to being acknowledged, let alone greeted, by total strangers may find this unsettling.
But returning the wave - or better yet, doing it first - will keep you from being tagged "Not from around here".
My friend Lisa and I, a couple of Big City gals, were in the Land of the One Finger Wave today. Read about our adventure in a country cemetery here.