Conditions control who can perform a transition and the circumstances under which they can perform this transition. If any part of a transition's condition fails, the user will not see the transition link on the 'view issue' page.
You can use JJupin JJUPIN and SIL to define a large set of conditions beside Jira's built-in conditions, by just adding a (k) SIL Condition to the transition and publishing the workflow, as described here.
Below are just a few common examples:
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