A hand gesture characterized by an
individual forming a closed fist with one hand and extending
the index finger to the proximal interphalangeal joint only. The joint should be flexed so the distal phalange points inward toward the palm.
The gesture is executed when two participants each form this fist and lightly tap their PIP joints together.
Often initiated by one person doing or saying something
really cool and the other person recognizing and respecting that action by holding up their fist as described above and saying "knuck".