You control access to the Library folder in the same way as any repository folder by granting permissions. By default, all users can see the Library folder and have updates pushed to them as necessary, but only administrators have the right to modify the glossary and other library models.
Since the library models and other documents are intended to be a reference to guide users, many administrators will want to closely control who can edit them. It is common to create a Library Administrators group with Write permission on the folder. Sometimes a separate Glossary Administrators group is created and Write permission on the glossary model is restricted to this subset of administrators.
For further information about permissions, see Granting Access Permissions on Repository Items.