A more thorough explanation:

Mouthpiece is a slang term for a lawyer, especially a criminal defense lawyer. It means that the lawyer is seen as the spokesperson for their client.

However, the term is not a positive one when applied to lawyers. It suggests that the lawyer lacks integrity and represents criminal clients without caring for justice to be served.

For example, in the case of Rudin v. Dow Jones & Co., the term mouthpiece was used to describe a lawyer as a "puppet, cat's paw, tool, instrument; operative, front, mercenary, servant, hireling, henchman." This calls into question the lawyer's sense of professional responsibility.

In summary, the term mouthpiece is a negative slang term used to describe a lawyer who is seen as lacking integrity and representing criminal clients without caring for justice to be served.