I believe what you are asking is what is laminitis- if so it is a condition that damages the bonds between the dermal and epidermal laminae in a horse's hooves, or the things that hold the hoof on. Severe cases of laminitus are known as founder, which is BAD.
Laminitis can be divided into three categories, cronic laminitis, usually the result of poor trimming and diet, acute laminitis which comes on very suddenly, usually the result of severe collic or a large dose of sugary food (can also be produced by contact with any part of a black walnut tree) and finally, 'road founder', which is the result of physical trauma.