Bounce rate is the rate at which people stay on or leave your website.
The longer someone stays on your website the lower your bounce rate and the shorter someone stays on your website the higher your bounce rate.
You want as low as a bounce rate as possible. Google search takes into account your bounce rate when deciding where to or how high to rank your content.
If you have a really high bounce rate, meaning people aren't staying on your website for very long or clicking the back button within a few seconds or minute of landing on your website then you will rank lower in google search.
If someone stays on your website longer then it most likely means your content is good and should rank higher.