Uninterested is the opposite of interested. It simply means you have no interest in something:
In casual spoken English, we tend to say “not interested” for the word uninterested.
The word disinterested means somebody is neutral. They have no bias (opinions that could unfairly influence their judgment). If two people are having an argument, they should present the case to a disinterested third party who can give a clear and fair evaluation of the situation.
However, some people do mistakenly use “disinterested” where “uninterested” would be more accurate.