This stands for long distance relationship. Basically, with the advent of the Internet, the concept of LDRs gained in popularity because frequently, or actually most of the time, the person you met on the 'net would live far, far away. So the LDR was invented, and it was quickly shown (through scientific observation of laboratory tests) that LDRs are bad for your health, and are doomed to failure 90% of the time. The remaining 10% are either lies or amazing luck, but they act as a carrot for future fools.