While we may be tempted to define a bounce as a single-page visit, a much better definition is a single-hit session.
Let’s first examine hit. In Google Analytics, a hit corresponds to any data that is sent from your website (or app) to the Google Analytics servers, including:
• physical pageview (or screen view)
• virtual pageview
• Ecommerce transaction
• tracked social interaction
If three users arrive on your home page and respectively play a video, download a PDF, and click through to your Twitter page, and you have those actions tracked as event, virtual pageview, and social, those sessions will not count as bounces, even if the users do not view any other physical pages.
Now, why session instead of visit?
If a user arrives on your site, views one page, speaks on the phone for 31 minutes, and then accesses another two pages, Google Analytics records two sessions for that same user, with the first session counting as a bounce. The visit consisted of three pageviews, but in the first session, there was only one pageview.
For these reasons, in defining bounce, hit is more accurate than page, and session is more accurate than visit.
It’s just one definition, but it encapsulates two important concepts in Google Analytics.