If you turn on the setting for Approved by default, as soon as a student adds an entry to a glossary, this entry will appear in the glossary. If it's turned off, the teacher will need to approve each entry.

If you turn on this setting and students add entries that you think are inappropriate, you can always delete these entries and turn this setting off.

If Approved by default is turned off, new terms will await the teacher's approval before being added. In the following screenshot, take a look at the link in the upper-right corner, Waiting approval(1):