Backlog generally refers to a list of requirements to fulfill while making a product. Requirements may refer to user stories, particular product features, tasks, and so on.
In YouTrack, backlog is a part of Scrum practice implementation, when you see tasks related to a sprint on the board. Following Scrum concept, tasks shall be related to a particular sprint or remain unscheduled in a backlog.
By default, YouTrack creates a saved search for you as soon as you create a new agile board. This is a search for
YouTrack replaces <project> with the actual name of your project, and makes this saved search available. You can see it in the left-hand column as you look at the issues list:
YouTrack uses the saved search to form a backlog out of issues you have in your project. It assumes that you use Fix version field to define a sprint that the issue belongs to, and that you need a backlog made of issues that do not belong to a particular sprint (i.e., with no Fix versions set).
To customize a search query that YouTrack uses to what you wish to make a backlog of, hover over the name of the saved search in the list and click the pencil icon. The following configuration dialog appears:
To see issues that are in the backlog now, click the sheets icon on the left-hand side of Agile board:
You can configure your board to use another saved search as a backlog for that particular board. Change it in the board configuration Saved search to show as backlog (see the last line of settings on the screenshot below):
The easiest way to prioritize your backlog is to do it from the issues list (not from Agile board view). To do that, click the corresponding saved search to the left of the issues list, hover over the issue, and then drag it to the desired position.
The higher the position in the list, the higher the priority. However, the position does not impact any field value in the issues: it's just easier for developers to pick up new tasks from the top of the backlog.
The issues in the list are sorted based on the preferences you defined by manual sorting; all remaining issues are sorted by update time. If the issues were sorted manually, this is indicated by the thin blue line on the left-hand side of the issues list.
The order remains unchanged until the next prioritization. You also can reset the custom order by clicking the cross in the top left-hand corner of the issues list.
You can reorder your backlog right from the board. However, this mode is more suitable for planning individual sprints, as the backlog view on the board lacks important details that may be important for its prioritization.