Hey Sarwan,
A bounce rate can be defined as a percentage of sessions/(visits) where only one interaction occurs. It's actually measured by a first arrival of a visitor, and if there isn’t a second interaction within next 30 minutes – it counts as “a Bounce”."
So, in this way, if you're viewing a page, and leaves your browser idle or left that page open for longer than 30 mins, it will register as a bounce. And, if you continues to navigate after this delay, a new session will occur. Same applies, if you keep open the tab for a whole day.
See the attitude image for more understanding.
Hope this clear your confusion!
Umar