Hashtag is a text tag that can be set on a task, post or attachment. Those tags can be used to describe objects in detail, they can be searched for either in the address bar or in Search tab. Every object can be assigned virtually unlimited amount of tags.

The universe administrator can create a new hashtag in the administrator window on the Hashtag tab.

You can add hashtags to a task in task properties, in Hashtags area, or you can use inline editing to add tags via Hashtag column.

To start a quick search on tasks containing a certain hashtag, you can left-click that hashtag with Ctrl button pressed, or you can right-click on it and select Search by hashtag from the menu. This will open Search tab with set criteria and search results.

You can search for several hashtags by Ctrl and left-clicking several hashtags. They will be searched for automatically.

You can add a hashtag while creating or editing a forum post.

Post hashtags are shown at the beginning of text.
By clicking on link, you will open a search panel with all project posts that have this hashtag attached.

You can add a hashtag to an attachment during creation/editing a forum post containing that attachment.

Kindly note, that there is a difference between tags and hashtags in Cerebro.