Bounce Rate
The percentage of visitors who leave a page without taking any further action, viewing no other page and triggering no event.
Bounce rate measures single-page sessions: someone lands, does not click anything else, and leaves. It is a page-level signal of whether the content matched what the visitor expected, not a judgment on the whole site.
A poorly timed popup, especially one that fires immediately on page load, can inflate bounce rate by giving visitors a reason to leave (or to trigger an ad blocker) before they have read anything. A well-timed exit-intent popup, by contrast, only appears after the decision to leave is already made, so it cannot make bounce rate worse and occasionally recovers a visitor who would otherwise have bounced.
Bounce rate and conversion rate pull in different directions when a popup is too aggressive: it might raise conversions among visitors who stay while raising bounces among those who leave immediately because of it. Watching both together is the only way to tell if a popup is a net gain.
See it in practice