A pathological liar is usually defined as someone who lies incessantly to get their way and does so with little concern for others. Pathological lying is often viewed as coping mechanism developed in early childhood and it is often associated with some other type of mental health disorder. A pathological liar is often goal-oriented (i.e., lying is focused - it is done to get one's way). Pathological liars have little regard or respect for the rights and feelings of others. A pathological liar often comes across as being manipulative, cunning and self-centered.
A compulsive liar is defined as someone who lies out of habit. Lying is their normal and reflexive way of responding to questions. Compulsive liars bend the truth about everything, large and small. For a compulsive liar, telling the truth is very awkward and uncomfortable while lying feels right. Compulsive lying is usually thought to develop in early childhood, due to being placed in an environment where lying was necessary. For the most part, compulsive liars are not overly manipulative and cunning (see, Pathological Liar), rather they simply lie out of habit - an automatic response which is hard to break and one that takes its toll on a relationship (see, how to cope with a compulsive liar).
What kind of liar is Hillary Clinton?? Can she stop lying for one month in her life???
That is the true mystery...