A DX-pedition is an expedition to what is considered an exotic place by amateur radio operators, perhaps because of its remoteness or because there are very few radio amateurs active from that place. This could be an island, a country, or even a particular spot on a geographical grid. DX is a telegraphic shorthand for "distance" or "distant".
Read more about DX-pedition: History, DX-peditions and Awards, Locations, Equipment and Operation, Contests, DX-peditions With Most Contacts