When you create a new project, a new Glossary is created, and the project becomes associated with this Glossary.
However, you're able to change which Glossary a project is associated with, or associate multiple projects to a single Glossary (though a project may only be associated with one Glossary at a time).
To associate a project with a Glossary:
Head to your Glossaries from the main navigation
Click on the glossary you want to associate a project to, and click on the Add/Remove projects . You'll see a list of all the projects in your organization.
Check the box next to a project to associate it with that glossary. If a project was associated with another Glossary previously, it'd now be associated with the new Glossary.
Click outside the box to finalize your changes.