Moral turpitude refers to crimes or actions that are considered to be vile, or seriously against the moral standards of society. In the context of the law, people who commit crimes of moral turpitude can face lengthy jail sentences. Also, people who wish to obtain green cards can be rejected if they commit crimes of moral turpitude.
Crimes of moral turpitude include rape, robbery, forgery, etc. The term "moral turpitude" is not actually used in the charging of people with crimes. Instead, the person is simply charged with the name of the crime. However, moral turpitude simply refers to any crime that is considered seriously immoral or depraved. The moral context is used in this term to highlight the fact that whatever crime the term is being used in reference to is something that is morally wrong and not acceptable in a civilized society.