Something that's reported is announced or stated. The reported reason for your teacher's absence from school might be the flu.
When two warring countries are reported to be starting peace talks, you'll probably hear actual reporters talking about it on the news. Sometimes the adjective reported implies that what's being stated might not be entirely true: "The reported casualties of the bomb are small, but some citizens claim there were many more." The root of reported is the Old French reporter, "to tell, relate, or bring back," from the Latin reportare, "carry back or bring back."