Project owners can configure the set of labels that are offered to members of a project. To edit the predefined labels, click the "Administer" tab and the "Issue tracker" sub-tab. Use the text fields to configure the set of issue statuses and labels that will be offered.
For example, if your project is building a graphics driver, maybe you would like to label some of your issues with Depth-16bit, Depth-24bit, and/or Depth-32bit.