Slow unchosen movement away from true — how records diverge from ground when nobody measures; named so it can be caught.
Old Norse drift (a driving, a pushing motion), related to drīfa (to drive); a slow, largely unchosen movement away from where a thing started.
A slow, unchosen movement away from what is true, the way records lean away from the ground beneath them when nobody keeps measuring. Drift is given a name here precisely so it can be caught.