According to Wikipedia: "ley lines are straight alignments drawn between various historic structures, prehistoric sites and prominent landmarks." Some people who believe in Ley Lines believe that these lines hold some kind of magical or sacred energy.
The idea of Ley Lines first emerged in the 1920s via the work of Alfred Watkins. Originally, Ley Lines were used only to describe the prehistoric landscape of Britain, claiming that prehistoric peoples used surveying and geography when building historical landmarks such as the stonehedge.
Later revivals of the Ley Line theory attributed the existance of these lines to something spiritual such as the Chinese “dragon lines” or the Native American “spirit paths." Others claim that these lines are just pure geographical coincidence. And yet others believe that Ley Lines align with Earths geological features such as fault lines, underground waterways, or natural magnetic fields.