Not interested in something; having no concern for or curiosity about something.
From 'un-' (not) + 'interested' (having one's attention engaged). In modern English, this is often confused with 'disinterested' (impartial), though they have different meanings.
Grammar nerds spend a lot of time arguing that 'uninterested' and 'disinterested' mean different things—and they're right! A judge should be 'disinterested' (impartial), while a bored kid is 'uninterested' (not caring), but most people use them interchangeably now, which would make a copy editor's head explode.
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