On this page:
Labelling allows you to categorise an issue(s) in a more informal way than assigning it to a version or component.
課題を表示すると、課題のラベルは「詳細」セクションに表示されます。
スクリーンショット:課題内の「詳細」セクション

If your JIRA administrator has added any custom fields of type 'Label', they will be shown below the 'Labels' field. For example, if you are using GreenHopper, a field called 'Epic' will be shown (see the GreenHopper documentation on Working with Epics. |
You can click a label (e.g. 'doc' in the above screenshot) to jump to the Issue Navigator and see a list of all issues which have that label. |
その他の利用方法:

You can also add a label when you create or edit an issue.

You can also remove a label when you edit an issue.