Glossary
Short definitions for the words that show up in every analytics-migration project. Each entry compares how GA4, Plausible, Matomo, and Fathom handle the concept differently — because the gap between vendors is usually where parity reports go wrong.
Unique visitors
How GA4, Plausible, Matomo, and Fathom each count a "unique visitor" differently — cookies vs fingerprints vs daily salts. Why the same site reads ~7 % different across tools.
client_id
GA4's per-browser identifier, how it deduplicates users across sessions, and what migration to cookieless tools loses in the process.
Engaged sessions
GA4's 10-second-active heuristic and what replaces it in the privacy-first stack — usually a "scroll 90 %" goal or visit_duration > 30s threshold.
Cookieless inflation
Why cookieless tools count more unique visitors than cookied GA4. Daily salt rotation, fingerprint+IP hashing, and the typical +5–12 % gap.
Adequacy decision
EC adequacy decisions: which countries are on the list, what they mean for analytics vendors, and why Schrems II hits Plausible (Estonia) and Fathom (Canada) differently.