''This term appears repeatedly on the CppHeresy page.  Can someone define it?''

If you are mathematically inclined, this may help:

http://www.itc.univie.ac.at/~hans/Columbus/documentation/fulldoc/mcscf.txt

"A microiterative method is used to solve for the wave function corrections."  

"This procedure involves subspace representations and reduced equation solutions similar to the Davidson diagonalization method.  This option allows printing of the micro-iterative convergence information and matrix-vector products for the Hessian matrix block with expasion vectors."

If not mathematically inclined, you might say: "Plain English Please"