Page Speed

Page speed is not a single metric but an umbrella name for the set of measurements that describe when a page becomes visible and when it becomes usable.

The umbrella splits into three questions: when did something appear on screen, when did the layout stop moving, and when did the page answer the user. A persistent source of confusion is that PageSpeed Insights shows two things at once, a lab score out of one hundred that is a weighted composite of several metrics, and above it the field data from real visitors; the two often disagree, and it is the field data, not the score, that counts in Google's assessment. The expensive mistake is chasing that score: deferring scripts the visitor actually needs can raise the number while making the real experience worse. Page speed is meaningful only when it is tied to measured behaviour rather than to a grade.