Binary Orbit is a trait in Destiny 2 that can appear on 58 weapons. There is also an enhanced version with a stronger effect.
What Binary Orbit does
Elemental final blows opposite this weapon increase damage for a short duration. Darkness final blows boost Arc, Solar, and Void weapons. Light final blows boost Stasis, Strand, and Kinetic weapons.
Enhanced version
Elemental final blows opposite this weapon increase damage for an improved duration. Darkness final blows boost Arc, Solar, and Void weapons. Light final blows boost Stasis, Strand, and Kinetic weapons.