It has to do with a nerve in your lower back, almost at your rear-end. It's called the sciatic nerve.
If it becomes aggravated (pinched or something), it can cause pain in your lower back, hips, and legs.
I'm not sure how they treat it though.
*Pain caused by a compression or irritation of the sciatic nerve by a problem in the lower back is called sciatica. Common causes of sciatica include the following low back conditions: spinal disc herniation, degenerative disc disease, spinal stenosis, and spondylolisthesis.
Applying counter pressure to location of sciatic nerve pain will provide temporary relief. This method may be utilized by applying 2-minutes of pressure to sciatic, using a solid object in the area of pain (ex. a fist or tennis ball) pressed against another solid surface (ex. wall).*