means Feeling no preference, concern, or interest either way — neither for nor against.

from From Latin indifferens, joining in- ('not') with differens ('differing, making a difference'), itself from differre, 'to carry apart' (dis-, 'apart,' plus ferre, 'to carry'). So at root the indifferent is that which 'makes no difference' — the thing where neither side tips the scale. It reached English through Old French in the late Middle Ages, first in the genuinely neutral sense of 'impartial, not partial to either side,' and only later cooled into the modern chill of simply not caring.