This custom fields allow you choose issue like value of fields. The list of values is configured using a JQL query in the admin section.Three types of these fields are available for use:
Linker Issue Custom Field is single select list from issue list.
Multi Linker Issue Custom Field allows you to select multiple issues as the field value.
Linked Issue Custom Field display issues only in read mode.
Want more information for configuration query fields? Check out our administrator's guide on how to.