An SEO glossary of terms every marketer should know in 2026
A practical, current glossary covering the essential SEO terminology every marketer should be comfortable with, from foundational concepts to 2026-specific terms.
6 min read
Google offers several distinct tools for measuring Core Web Vitals, each serving a slightly different purpose, and understanding the difference between lab data and field data explains why they can sometimes show meaningfully different results for the exact same page.
PageSpeed Insights: combining both data types
PageSpeed Insights shows both real-world field data (from the Chrome User Experience Report, where available) and a fresh lab test (powered by Lighthouse) in a single report, making it the most convenient single tool for a quick, comprehensive check.
CrUX (Chrome User Experience Report): real-world field data
CrUX aggregates real, anonymised performance data from actual Chrome users who visited your page, reflecting genuine, varied real-world conditions (different devices, connections, locations) rather than a single simulated test scenario — this is the data source underlying Search Console's own Core Web Vitals report.
- Reflects real visitor conditions across diverse devices and connections.
- Requires sufficient traffic volume for a given URL to have reportable data.
- Updates on a rolling basis reflecting recent, genuine visitor experience.
Field data tells you what actually happened to real visitors. Lab data tells you what happens in one specific, controlled, simulated scenario — both are useful, but they answer genuinely different questions.
Lighthouse: controlled lab testing
Lighthouse runs a single, controlled simulated test under specified conditions (a particular simulated device and connection speed), useful for diagnosing specific technical issues and testing the impact of a change immediately, without waiting for real-world field data to accumulate.
Why the tools can disagree
A page might perform well in a single Lighthouse lab test but show poor field data, if real visitors commonly use slower devices or connections than the lab test's simulated conditions — or vice versa, if the lab test happens to simulate unusually poor conditions relative to your actual visitor base.
Frequently asked questions
Which tool does Google actually use for ranking purposes?
Google has confirmed it uses field data, similar to what CrUX and Search Console's Core Web Vitals report show, rather than a single lab test result, for its actual ranking assessment.
Why does my page have no field data in PageSpeed Insights?
CrUX requires a minimum volume of real Chrome user visits to generate reportable data for a specific URL — lower-traffic pages may show only lab data as a result.
Should I optimise based on lab data if field data is unavailable?
Yes, lab data remains a reasonable proxy and useful diagnostic tool in the absence of sufficient field data, though it should be treated as directional rather than a guaranteed reflection of real visitor experience.
If you want help interpreting your Core Web Vitals data across these different tools, talk to our team.
The takeaway
Trust Search Console and CrUX field data over a single Lighthouse lab test when the two disagree — field data reflects real visitors under real conditions, while a lab test reflects one simulated scenario.
Written by Fibvo — Bengaluru and Erode, India — working with clients in other time zones. Questions, or think we have it wrong? Tell us.
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