Email bounce means the rejection of an email by the recipient server. There are soft bounces, i.e. temporary bounces that are typically fixed after some time. A usual soft bounce is Mailbox is full. Hard bounces mean a permanent problem. For example a non-existing mailbox.
Sending emails to bounced addresses is an undesirable practice that could harm your delivery rates. That's why Incomaker not only informs you about bounce rates in your reports but also stops sending emails to bounced addresses automatically after several attempts.