These are the three numbers most people see first when they open Google Analytics. They're also the three numbers most commonly misread.
What a user is
A user represents a distinct browser or device that has visited your site. GA4 identifies users through a combination of cookies, device identifiers, and, when available, a user ID you can provide. One person using two browsers, or the same browser on two devices, can register as two different users. GA4 introduced a "blended" identity method that attempts to reconcile these, but it's an estimate, not a perfect count.
What a session is
A session is a group of interactions that happen within a defined time window. In GA4, the default session timeout is 30 minutes of inactivity. If the same user returns to your site after 31 minutes of doing nothing, that counts as a new session. Sessions also reset at midnight. One user can generate multiple sessions in a single day. This is why your session count is always higher than your user count.
What a pageview is
A pageview is recorded each time a page is loaded or the page URL changes. On single-page applications, pageviews need to be configured manually because the URL doesn't always change when content does. Pageviews are the most granular of the three: one user, one session, but potentially many pageviews as they navigate through your site.
Why the three numbers diverge
Imagine one person visits your blog Monday morning, reads two articles, closes the laptop, then comes back that evening to read a third. That's one user, two sessions, and at least three pageviews. The numbers tell different parts of the story. Users describe reach. Sessions describe visit frequency. Pageviews describe depth of engagement.
None of them is "the right metric." The right one depends on what question you're trying to answer.
Quick reference