Kosovo is a province in southern Serbia. It is Serbian, until it claims its independence, which surely is going to happen.
There was a big battle of Kosovo in 1389, where both Serbian and Turkish emperor lost their lives.
The Serbs anticipate that event very much.
Kosovo is, though, the center of drug dealing, sex trade, weapon black market, etc, for all the other countries in the world, e.g. USA, as one of the biggest.
People that live there are popularly called Shiptars
. They often don't have power, water, homes, education, teeth or anything else.
'Kosovo is Serbia' (Kosovo je Srbija) - often used by patriots that don't want its independence. Seen in almost every graffiti art in Serbia.