Sound
Decay
Also called ringing, overhang
Decay is how a sound fades after it is struck: the trail of a cymbal, the ring of a piano note, the reverb of a hall. Natural decay sounds spacious; cut short it sounds dry, and added ringing sounds muddy.
Driver resonances add decay that was not in the recording, which shows up in a waterfall or cumulative spectral decay plot as ridges that persist. In the bass this is heard as boom or overhang; in the treble as a metallic sheen.
In rooms, decay is the reverberation time, and room treatment exists largely to control it. On headphones, pad material and the cup design decide much of it.