definition v5 of error

Error is the human-made concept that distinguishes an actual outcome from its expected, intended, or prescribed value. The construct operates by establishing a reference — a spec, a model, a test, a prior, a target — and then measuring the deviation of actual behavior from that reference. The error is the difference itself: what the system failed to match. It persists because it is the load-bearing unit of correction — quality control, debugging, verification, and every form of corrective reasoning are built around the act of detecting error and reducing it. The error can be measured against different kinds of reference, and each reference choice carves a different parameter: the gap between actual output and intended output, the gap between observed and predicted, the gap between current state and goal state.