ADR stand for "Automated" or "Automatic" Dialog Replacement. 

Dialog that cannot be salvaged from production tracks must be 
re-recorded in a process called looping or ADR.  

Looping originally involved recording an actor who spoke lines in 
sync to "loops" of the image which were played over and over along 
with matching lengths of recording tape. ADR, though faster, is still 
painstaking work.  

An actor watches the image repeatedly while listening to the original production track on headphones as a guide. The actor then re-performs each line to match the wording and lip movements. Actors vary in their ability to achieve sync and to recapture the emotional tone of their performance.  

Marion Brando likes to loop because he doesn't like to 
freeze a performance until he knows its final context. 
(People have said that one reason he mumbles is to make the production sound 
unusable so that he can make adjustments in looping.) 

ADR is usually considered a necessary evil but there are moments when looping can be used not just for technical reasons but to add new character or interpretation to a shot. Just by altering a few key words or phrases an actor can change the emotional bent on a scene. 

Diaglogue Editor/ ADR Recordist Chris Ward, Supervising Sound Editor Mike Hopkins, Co-producer/Screen writer Philippa Boyens and actors Jack Black, Colin Hanks, and Thomas Kretschmann talks about ADR

The way ADR is treated and approached is symptomatic of how little respect sound gets in the movies. You march the actor into a cold sterile room and usually give them no time to get into the character or rehearse. They are  expected to just start performing a few minutes after they walk into the room. The emphasis is almost always on getting the dialogue in sync instead of getting the  right performance. Of course the majority of the actor's brain is then occupied with whether his lips are flapping at exactly the same rate as they were on the day that the camera was rolling. It is no wonder that most ADR is not very good. In the final mix, directors almost always prefer the production sound, even if it is noisy and distorted.

One of the things you do with ADR to make it sound more like production sound is to pitch it up. ADR is almost always delivered at a lower pitch because the actor doesn't have the energy he/she had on the set.  In the excitement of the shooting set the actor tends to talk louder and higher. In an ADR session, the director typically has to push the actor to get them anywhere near the level of vocal performance that came from the set. 

If the recording of ADR were treated more like shooting the movie it would almost certainly be better.  Recording it in more authentic environments (instead of studios) tends to help the actors' performance enormously.  Environmental noise is a problem whenever you record outside of a studio, but well worth the trade-off in my opinion

Read "Orson Wells and ADR" 
 

Dialog Replacement 101 - Never Underestimate the Value of Good Dubbing By Blair Jackson, Mix mag Nov 2006

Dialogue Editing for Motion Pictures: A Guide to the Invisible Art by John Purcell (2007) A comprehensive and detailed guide to the craft of dialogue editing. Recommended!! >> You can buy this book at Amazon.com  Amazon UK Amazon Ca

Ambience 

Ambience pertains to the pervading atmosphere of a place. (Often more of a psychological, rather than technical description) 

Ambience is widely used as a synonym for ambient sound. Ambient sound consists of noises present i the environment.  

In film and video sound production term Ambience usually means  the background sound accompanying a scene.  

Ambience is used for background sounds.. 

(1)  present in the original production recording (a better term for it is presence)

(2) deliberately added in sound-effects editing in order to provide an acoustic space around the rest of the dialog and sound effects.

Subjective Ambience: 
In the trial scene of Philadelphia -  instead of using reverb to a voice as the convention says for hallucinating  -  sound designer Ron Bochar used subjective ambience. He dropped the previous room tone and shifted the ambient sound.  He also changed the spatial placement of the ambient sound -  from left, right, and center speakers to surround speakers.  

Ambience helps establish the scene and works editorially to support the picture editing by, for example, staying constant across a picture cut to indicate to the audience that no change of space has occurred, but rather only a simple picture edit. Conversely, if ambience changes abruptly at a picture cut, an indication is made to listener that the scene also has changed.  

• Elisabeth Weis: Creating sounds for Demme 

• R. L. Mott: Sound effects radio, TV, and film p 202 

• Tom Holminson: Sound for Film and TV 
• Reviews at Amazon books 

Philadelphia

Silence of the Lambs