Short term allocations can be used where a resource might be used and isn't available to be allocated to an event over that time.

Some examples of this might be for:

To add in short-term allocations, first view the resource and then click the 'Add short-term allocation' link at the bottom of the page. From there, complete the required information, including the dates & times it will be unavailable for, as well as the contact details for the resource during that time.