Traffic
Bounce
Also called single-page session.
Bounce is a session that ends after one pageview, or in newer models a session that never passes an engagement rule. It is a property of one visit, so you count bounces and then divide to get a rate.
How it is measured
Under the classic rule a session is a bounce when it has exactly one pageview and no interaction event. Under an engagement rule it is a bounce when it lasts under a set time, has one page, and fires no conversion. Counting is done per session, so a single visitor can bounce on Monday and not on Tuesday.
Tarsier works out a bounce on the server from a visit with a single pageview. Custom events never change visitor, visit or bounce counts, so a phone tap tracked as an event shows up in its own goal and does not rescue the visit from the bounce column.
Worked example
A plumber's one-page site gets 52 phone-link taps in a month. Most of those visitors land on the home page, tap the number and leave without a second page. Under the classic rule every one of them is a bounce, yet each is a lead.
The owner fires a tap event for the call button and reads it as a goal beside the bounce figure. The bounce rate stays high, and the goal shows 52 calls. Together the two numbers tell the true story.
How it differs
A bounce is one session outcome. Exit is where any session ended, including long ones. A bounced session is always an exit on the landing page, but most exits are not bounces because the person saw several pages first.
Common errors
Calling a bounce a failure. Applying the term to a single-page site and being alarmed. Ignoring that a read-and-leave article is a good answer. Mixing the classic rule with an engagement rule between reports. Counting bots as bounces.
In practice
Pick the rule your tool uses and record it. Add an event for the action that counts as success on single-page layouts, such as a call tap or form submit. Then review bounces by landing page, not as a site-wide number.