From LQWiki

the opposite of insert

To eject something (usually a cd, dvd or floppy) means to remove it from the computer, not access the content, and usually replace the device to read more data.

You can eject by either pushing a button on the drive or virtually. In linux you need to unmount the device to eject it. Most user friendly distros treat this as the same deal.

It is a good idea to eject media before a reboot so that the computer doesn't try and install from the device.