According to the International Organization for Standards (ISO) refinements 3950 to the FDI system, 05 refers to:
International Organization for Standards (ISO) has added refinements (ISO 3950) to the FDI system to designate areas of the oral cavity and to provide 'sextants' as with the CPITN. 
00 whole oral cavity 
01 maxillary area 
02 mandibular area 
03 upper right sextant 
04 upper anterior sextant 
05 upper left sextant 
06 lower left sextant 
07 lower anterior sextant 
08 lower right sextant 
09 additional document
Upper right sextant
Upper left sextant
Lower right sextant
Lower left sextant