Qu'est-ce que Unique visitor ?

A unique visitor is one person counted once within a reporting period, regardless of how many times they come back. If someone visits your site five times this week, that is five sessions but one weekly unique visitor. It is the closest thing analytics has to "how many people saw this."

The catch is the word "unique." Cookie-based tools recognize returning people by reading back a stored ID, which breaks when visitors clear cookies, use private browsing, or reject the consent prompt. Cookieless tools identify visitors within a day using short-lived, non-reversible tokens, so the same person on Monday and Thursday counts as two visitors. Neither approach is wrong, but daily uniques and monthly uniques mean different things in different tools, so know which one you are looking at before comparing. The same person on a phone and a laptop is two visitors in almost every tool until they log in.

Uniques are the standard denominator for reach questions, while sessions and pageviews answer frequency and depth.