In Plain English
It is like counting visits that ended before a venue’s chosen definition of an engaged visit was met—but that definition depends on the measuring system.
Why it matters
Understanding bounce rate helps you make clearer SEO decisions without mistaking one signal or metric for the whole picture.
Example
In Google Analytics 4, a session that is not classed as engaged contributes to bounce rate; the metric is the inverse of engagement rate.
Common misunderstanding
A bounce is not automatically bad and definitions differ between tools. Someone may read a complete answer and leave satisfied, so interpret the metric with page purpose and other evidence.