DX is “distance”, today it generally means contacting amateur radio stations in far-away and rare places. On the HF (also known as shortwave) bands, DX stations are those in foreign countries. On the VHF/UHF bands, DX stations can be within the same country or continent, since making a long-distance VHF contact, without the help of a satellite, can be very difficult.
For award purposes, other areas than just political countries can be classified as “DX countries”. For example, the French protectorate of Reunion Island in the Indian Ocean is counted as a DX country, even though it is a region of France. The rules for determining what is a DX country can be quite complex and to avoid potential confusion, radio amateurs often use the term entity instead of country. In addition to entities, some awards are based on island groups in the world’s oceans. On the VHF/UHF bands, many radio amateurs pursue awards based on Maidenhead grid locators.