If you're indifferent about something, you don't care much about it one way or another. You might feel indifferent about politics, changing the channel whenever the TV news comes on.
People seem indifferent when they're obviously unconcerned — an indifferent observer of a tennis match is clearly not rooting for either player, and an indifferent voter might choose a candidate at the last minute by flipping a coin. A slightly less common meaning of indifferent is "unbiased or impartial," which you can see in its root, the Old French indifferent, or "impartial." In this sense of the word, we all hope our laws and legal system are indifferent.