noun, masculine
rest, remainder, leftovers, extra food; (especially) in a canteen, where using which, one can ask for some extra food from the cook or canteen service
“je peux avoir du rab ?” — Can I get some more (food)?
Related: en rab, faire du rab, saute-au-rab
Clipping of rabiot (“(originally fishermen and military cant) excess, remainder; (earlier) (1831) excess of fish remaining after rations had been imparted to the mates, (1859) soup soldiers often left over in their mess tin, (1832) an extra something which one can enjoy”). Further unclear, probably from (Gascon) Occitan rabiot (“little fish; leftovers from fishing”).