This is the inflammation of a bursa (pouch of fluid) that lies between the tendon of iliopsoas and the underlying bone. It is causes by a combination of over use and a tight iliopsoas tendon.
It causes pain over the front of the hip associated with movement, the pain may also be felt in the groin. It may be aggravated by walking, running climbing stairs and getting in and out of cars.
If you think you have this injury it is well worth getting it checked out by Mr Willis-Owen. In the mean time you should avoid any aggravating activities with may prolong the problem. It generally wont get better on its own. The first thing to do is reduce your activity and start hip flexor stretching.
Treatment involves first confirming the diagnosis then establishing the underlying causes. Options may include activity modification, physiotherapy, anti-inflammatories.