The short answer is that disinterested means unbiased, having no conflicts of interest, impartial. So a judge in a court should be disinterested, but not uninterested.
Using "disinterested" to mean "uninterested" has become more common over the past few decades, rather than using it in the older sense of "having no stake in the outcome, having no bias or partiality with respect to a conflict."
An example would be saying that someone was "disinterested" in what was happening on TV, or in music that was playing.