Settling time
The time after a seek when the head is still oscillating and must stabilise over the target track before any read or write may begin.
A seek does not end the instant the voice-coil motor has moved the arm to the right cylinder. The arm is a springy mechanical structure and rings by a few micrometres around the target; the servo has to damp that oscillation until the head sits still within a fraction of the track width. Only then is the margin small enough to write without corrupting the neighbouring track.
Settling time is therefore a hidden part of seek time and one reason short seeks are not proportionally faster — the move itself may be brief, but the settling takes roughly the same time regardless. Writing demands tighter tolerance than reading, so write seeks have longer settling.