( Expert )
11 November 2010
Moral turpitude is a legal concept in the United States that refers to "conduct that is considered contrary to community standards of justice, honesty or good morals."
The concept of moral turpitude escapes precise definition but has been described as an "act of baseness, vileness or depravity in the private and social duties which a man owes to his fellowmen, or to society in general, contrary to the accepted and customary rule of right and duty between man and man."  The specific acts that such a concept includes inevitably change over time, as general public acceptance or abhorrence of issues alters; for example, until recent times, a man engaged in homosexual behavior was still considered as engaging in "criminal behavior involving moral turpitude."
The classification of a crime or other conduct as constituting moral turpitude has significance in several areas of law. First, prior conviction of a crime of moral turpitude (or in some jurisdictions, moral turpitude conduct, even without a conviction) is considered to have a bearing on the honesty of a witness and may be used for purposes of witness impeachment. Second, moral turpitude offenses may be grounds to deny or revoke a professional license such as a teaching credential, license to practice law, or other licensed profession. Third, it is of great importance for immigration purposes, as only those offenses which are defined as involving moral turpitude are considered bars to immigration into the U.S.
Source : Wikipedia