Bind Mounts
Bind mount is a special type of file or directory binding feature. This means, a directory at a different location is bound to another location.
In Memory Bound
Normally mount points are configured in the /etc/fstab file. When system boots, every entry in this file is read and an instance of Mount Structure is created.
This is exactly what bind mount command does. It directly creates a new instance of this structure without making any changes to the file.
Since it's only an object in the memory, the mount information is lost during reboot.
This is exactly why they're also lost when containers are stopped.
Difference to soft and hard links
When we create soft and hard links, this information is stored on the filesystem itself. Whereas in case of bind mount, the information is just inside kernel memory.