DXing is the art of picking up, tuning in and listing to far-off radio stations. The “D” is for distance; the “X” is the unknown. DXers sometimes contact remote stations they pick up for reception reports; some collect the QSL cards that are sent in return.
Some of the major sites for DXing:
DXZone is the huge site with directories and links.
Glenn Hauser’s DX Listening Digest
Huge directory: SHORTWAVE, LONGWAVE, DC TO DAYLIGHT
John Wagner’s Shortwave Tips & Tricks
The NASWA WWW Shortwave Listening Guide is a searchable database.
“The Shortwave Numbers Mystery” describes a weird phenomenon that has been noticed on shortwave radio since the mid-’70s and has never been solved.
Other bands and frequencies
Beacon DXing: picking up nautical and aircraft beacons, oil and gas platform beacons, and so on.
DXing “downstairs” with Longwave DXing (frequencies below 500kHz)
One of the best forums for radio is radio-info.com where boards exist for various genres, markets and cities, and types of radio.
There’s also the old Usenet group, rec.antiques.radio+phono
For further reference
Illustrated article, “The Evolution of Radio” by The Schenectady Antique Radio Club.
If you want to get a reference book, get “The Comprehensive Guide to the World of DXing”.