Ley lines, a mystic phenomenon corresponding to the more scientifically observable phenomenon known as telluric currents, are flows of magical energy that occur in nature. Ley lines are flows of magical power allowing those who understand them to tap into their power. Places where multiple ley lines intersect constitute nodes of power, and the more lines intersect the greater the power of the node. Especially powerful nodes often become the location of sacred sites, which if nurtured over time may become very powerful magical places of power.
The Nemeton is a prominent example of a powerful node, as are many of the resting places of various Old Ones. Over time, such locations can cause the boundaries between the Earth and other realms to weaken, allowing gateways like Hellmouths to form.
A telluric current or "Earth current" is an electric current that flows underground or through the sea. Telluric currents can result from human activity, but only naturally generated currents are known to correspond to ley lines. These currents are extremely low frequency and travel over large areas at or near the surface of the Earth, forming complex patterns. These currents have various mundane applications, but what is most significant about them is the magical ley lines that they correspond to.