In some of our ticket rules, you can specify a condition or action as a "current user". What this means that the current user is the logged in user at the time the rule is executed.
For instance: Let's say you have a ticket rule that you want to know when a ticket is created and is open you would like to send an email to the current user letting them know.
The current user at this point can be the client submitting the ticket or even the agent depending on who created the ticket. If a regular user submitted the ticket, then the regular user would be the current user, but if the ticket was created by the agent then the agent would be the current user.