[otrs] what is "pending autoclose+/-" ?

Hi all. By default, OTRS create states like new/open/closed, its needed in process (although about difference between new and open I not guess straight away) Also it create states pending autoclose+ pending autoclose- how it work? what difference between this? Can the system work with scheme like this: agent answer on customer email, and if customer do not reply or send followup on that ticket again in 3 days, ticket auto-closing ? this scheme must be "by-default" without any agent actions. Or better use genericagent functionality? Mike