Usually someone who acts exactly like the Seinfeld character of Newman. Sometimes it can be even used as a nickname for said person. Most of the time, if your name is Terry, you could be nicknamed Newman by your friends.
A newman is another name for someone who is only partially spasticated/mentally challenged. It may not be a form of disablilty, but certainly does show signs of difference from a normal person Another obvious sign of being newman'd is having a tongue too big for your mouth, also, negative reactions from the female gender are a certainty. Most newmans are found in the london area, possibly due to pollution or living in a well