>Reentrancy: A program that may be called by another while it is already in the calling stack;
>

PMJI Jim,
It's been a long time since the theory classes but I thought 'reentrant' simply meant that more than one pointer (IP?) to a current program line is allowed, thus allowing more than one process to be using the same program code.
Does that ring a bell?
(Please tell me to go jump if i've missed the point here)