Here is an official definition from Professional Interpreting Enterprises in the Milwaukee area: http://www.pieinc-wi.com/cdii.html I will sum it up best as I can:
So you know someone, have a student, are yourself a minimal language user. You sign a little and even might talk a little in some situations. Point is, you are not fluent in American Sign Language and you are not able to use just Listening and Spoken Language to communicate. So, how does someone facilitate communication for you/your student/your friend,etc?
A Deaf Interpreter is part of a team. A hearing person is an interpreter and will listen to the spoken word and sign it into American Sign Language. The Deaf Interpreter then "reads" the signs of the interpreter and breaks the language down into even more basic American Sign Language plus gestures. Being Deaf him/herself allows the Deaf person to understand from the gut level how to manipulate this native language of American Sign Language. This type of tag team interpreting is not for everyone and may or may not be effective. It is just another wonderful option in the Communication Tool Bag. Why limit the possibilities!? If you or someone you know is struggling using a traditional interpreter, be sure to state what kind of signs you want-Signed Exact English(which is transliteration of spoken English to English on the hands), American Sign Language( which is translating spoken English to a new language, ASL ) or Pidgeon Signed English-ASL concepts in English word order without the word endings on signs. If this still is not quite right, then investigate a Deaf Interpreter. Know that YOU are the consumer and you have a right for your needs to be met.
Please comment if you have ever used a Deaf Interpreter or any interpreter at all.