Definition
The rotation of a helicopter rotor blade about its own long axis (the spanwise axis running from root to tip), which changes the blade's pitch angle and therefore the amount of lift it produces. Feathering is controlled by the pilot through the collective and cyclic, acting through the pitch horn and pitch change links at each blade.
Plain English
Feathering is when a rotor blade twists along its own length to change its angle into the wind. Twisting it more makes it grab more air and lift harder; twisting it less makes it grab less air and lift less. This is how the pilot controls how much the helicopter climbs, descends, or tilts.
Context Anchor
Seen in helicopter rotor system discussions, especially when describing how the flight controls change blade angle to control lift and direction.
Derivation
From the everyday image of turning a paddle or oar 'on edge' so it slices through the water — sometimes called feathering an oar. A rotor blade does the same thing in air: it rotates about its long axis to change how much air it bites.
Why Pilots Care
Proper feathering reduces drag on shutdown, protects the rotor system, and helps maintain rotor RPM in autorotation.
Analogy
It is like holding your flat hand out of a car window and twisting it. As your hand changes angle, the air pushes on it differently.
Intuition Check
Feather does not mean covering something with feathers here. It means changing the angle of a rotor blade by rotating it along its own length.
Example Sentence 1
When the pilot raises the collective, all rotor blades feather to a higher pitch angle at the same time, increasing lift across the disc.
Example Sentence 2
During autorotation training the instructor reminded the student to feather the blades smoothly on touchdown.