A "tourist advisory" is a warning issued by the US State Department when conditions exist in a foreigh country that potentially threaten the lives of American citizens visiting or living there.
For example, if some terrorist organization makes a public statement in Italy that they plan to kidnap Americans, the State Department might issue an advisory warning Americans it coult be dangerous to visit Italy. If civil war starts in some country there might be an advisory because it is just dangerous for any foreigner to be there.
Countries always lose tourism income when an advisory is issued bor that country because most travelers will not visit countries that have current advisories issued about them.

