Within Teamwork.com, you can enable tags on your site and specify whether non-administrators can create tags.
Click your profile icon in the bottom left corner of your site and select Settings from the dropdown menu.
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In the settings area, go to the General subsection.
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You will see an option to Allow tags to be used on your site. You also have an option to lock the editing of tags to administrators only.
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When you enable the tags option, you will also see a Tags area in the site settings menu for managing tags.
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For more information, see: Tag Options