What is an Ad-Hoc Acting Editor for Journal of Finance and/or PNAS? What is an Ad-Hoc Acting Editor for the Journal of Finance and/or PNAS? Is it similar to the special-issue editor? How to select that editor in paper submission?
A special issue editor would normally be referred to as a guest editor.  Most likely the “normal” editor suddenly resigned or otherwise cannot continue her or his duties for a while, and someone stepped in until a permanent editor is found or the regular editor returns.