DX is reliant on tropospheric ducting to get a signal even with the weaker antennas. it happens only in certain conditions in certain times of the year (usually late spring/early summer) but in my case i improved on the design of my RV's roof antenna with two large amps and a new set of cables. unlike DX reception i can consistantly maintain signals even if i have to wait until the sun sets first.
DTV/radio hobbyists sometimes use the term 'DX' to mean the hobby of getting as many channels at far away places as possible.