This is an inbuilt function function provided by PPWIZARD.
This function returns the name of of currently non-existing file which can be used as a temporary file.
If you want some control over the name of the file then you may pass a single parameter which is a filename with '?' in any positions where a "random" digit can be placed (example "IMP_????.TMP").
Note that it is possible to get the same value for 2 consecutive calls unless the parameter differs unless you create the first file before calling this function the second time.