meta name="description"

For all new installations edit conf/globals.php $sys_defd for a default, no matter what meta description for each page

For each subdirectory of the the /fragments directory it is a good idea to edit $_SESSION['currentDirPath']/robopages/metadesc
so each page in that subdirectory has slightly more specific meta name="description"

For each individual page in any subdirectory of /fragments, like the page generated by ?robopage=/Birds/_PIC7254_Dowitchers.jpg
you can edit a custom per-page meta description with by creating and editing a file named
/path1/path2/path3/fragments/Birds/_PIC7254_Dowitchers.jpg_metadesc