In amateur radio, DX means a distant station, often one in another country. DXing is the pursuit of such contacts: tuning for faraway signals, working them, and collecting confirmations. It rewards patience, good listening and a feel for propagation more than raw power.
The loop
The same loop applies to a rare expedition and to a station you simply have not worked before.
Stations are often counted as entities, which are not quite the same as sovereign countries. A remote island or territory can be its own entity even when it belongs to a larger nation. Awards such as DXCC count entities; see Awards and certificates. Check the program's current list.
What helps
A decent antenna. Even a simple wire at a good height, working at a low take-off angle, will beat a lot of power on a poor one. A beam is better still. See Ground effects and height.
Knowing the bands. Higher HF bands are good in daylight when conditions are right; lower bands carry long paths at night. The grey line around dawn and dusk can open unusual paths.
A way to find activity. DX clusters and the Reverse Beacon Network post stations as they are heard. See DX clusters, RBN and PSK Reporter.
Good receive. In DXing you hear many stations you cannot work. A quiet location and receiver, and a noise-reducing setup, matter as much as transmit power.
A willingness to wait. Rare stations may be on the air for only days. Expeditions and special events can draw large crowds; see DX etiquette and split operation.
Calling CQ DX
Two small rules of manners apply on voice:
Break in short. Answer CQ DX only from outside the caller's area.
A US station calling "CQ DX" is asking for stations outside the contiguous 48 states; answer only if you are one. If you are in the lower 48, you wait for a DX station to call CQ, or you call it directly.