Some types of data, like coupons, have a limited duration. In other cases you may just want to limit the time an item is listed in your directory, either to encourage freshness or encourage people to pay to keep the topic longer.

The 'expirations' switch enables/disables the option to set an expiration date for topics on the 'submit topic' or 'edit topic' pages. Normally this will be done by directly typing a date or number of days, but by checking the 'incriment options' subswitch you can present a dropdown selector from which the user will choose a number of days to expiration or a number of days to renew for.

At Admin Panel -> Members -> Manage Usergroups you can specify for each usergroup how many times they can renew an expired topic, and for how many days. The days set here will also be used to determine the selector values when you have the 'incriment options' switch on, unless you set a default days to expiration. In order to renew the user will simply edit the topic and select the radio button to renew.

At Admin -> Topics -> Topic Settings you can set a default number of days to expiration which will apply to new topics unless overridden.