Term Kind Topic What it is
Beacon Survivorship RUM Survivorship Bias, Abandonment Bias concept Real User Monitoring The bias in field performance data caused by users abandoning a page before the measurement beacon is sent - so the slowest sessions are excluded and the metric improves as the experience gets worse.
Field Data Versus Lab Data concept Real User Monitoring The difference between what real users on real devices experience and what a synthetic run measures, and why the second is systematically optimistic.