What Are The "Lines"?

Pretty much everyone knows that the strap between the bridle and the rider's hands is called the "rein" or "reins." (It's plural even though some English reins are a single strap).

So, what are the lines?

When driving, you don't call the strap between your hands and the bit the "reins." You call it the lines - perhaps due to its much greater length. (This is a common mistake made by writers).

In this picture, for ground driving, the lines are tucked through the "saddle" - yes, the thing resting on her back is still called that.