TERMINOLOGY USED IN WX BRIEFING; MARGINAL VFR; QUESTIONED. UNABLE TO FILE IFR TO NDB.

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DURING A STANDARD WX BRIEFING FOR A LCL IFR FLT; THE WX BRIEFER TOLD ME THAT THE WX WAS 'MARGINAL VFR' 2000-2300 BROKEN WITH 3-4 MI IN FOG. IS THE TERM 'MARGINAL VFR' A COMMONLY (LEGAL) TERM FOR A STANDARD WX BRIEFING OR WHEN WX IS GIVEN BY ATC? PLEASE LET ME KNOW! THANK YOU. I ATTEMPTED TO FILE AN IFR FLT PLAN FROM 3R8 TO AEX BY FILING 3R8 DIRECT CAMPI (WHICH IS THE LCL) NDB AND THEN DIRECT AEX. THE ATC COMPUTER WOULD NOT ACCEPT CAMPI AS A FIX. FSS SAID I WOULD NEED TO FILE DIRECT OR TO AN INTXN ON V114; BUT I CAN'T FILE DIRECT DUE TO 3R8 BEING OUT OF THE SVC VOLUME. IT WOULD BE EASIER TO FILE CAMPI NDB AND THEN DIRECT; INSTEAD OF TRYING TO FIND AN INTXN UP TO 25 NM AWAY. WHY CAN'T I FILE TO A NDB? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED AIM DEFINITION OF MARGINAL VFR; 1000 TO 3000 CEILING AND 3 TO 5 MI VISIBILITY. FILING IFR TO AN NDB LIMITED BY WHAT HAS BEEN PROGRAMMED INTO THE COMPUTER. IF THE NDB IS NOT IN THE COMPUTER; THE PLANNED ROUTING WILL NOT BE ACCEPTED. INFO FROM PROC SPECIALIST AT FSDO. RPTR USING INFO FOR A GND SCHOOL CLASS.