A Speech impediment is a type of communication disorder where normal speech is disrupted. It is an umbrella term used to describe different conditions resulting in someone unable to produce clear speech. It  can be both congenital (born with it) or acquired due to another pathological condition. 

The problem can lie in any part of the pathway in production of speech. It could be the brain, ears for listening, structures of the mouth. In some cases it is easy to understand such as in a child who has had a stroke or cleft palate. In other cases, it is due to the complex neurological processes in the brain that dictate how the mouth produces sound. 
 

There are also some causes where the exact pathology is unknown, idiopathic.