Ad lib from the latin phrase ad libitum, meaning at one's pleasure, is something improvised in speech, a spontaneous spoken addition
or revision to the written script. Though some jobs may require improvisation, at the client's request, an unsolicited ad lib is seldom
welcome.

ADR or automated dialog replacement is simply the recording of dialog for a previously shot scene in television or film. ADR recording generally occurs in a professional studio setting during post production. Although originally ADR referred only to post-production dialog recorded to replace original dialog in a scene, it is now widely used for all dubbing, including previously unrecorded multi-language tracks and background conversations added in post production. ADR may or may not be provided by the original actors seen in the live action images.

An air check is any recording of a broadcast radio program. Air checks are generally used for archiving or as a demonstration (demo) for on-air talent. Often these recordings are 'telescoped' or 'scoped' as it is commonly referred to, meaning that music and promotional elements are skipped over in favor of just the air talent's portion of the program.

An information form that is represented by a continuous and smoothly varying amplitude or frequency changes over a certain range such as voice or music.

An audio book is a recording of the contents of a book read aloud. It is usually distributed on compact discs (CDs), cassette tapes, or digital formats (such as mp3). The term "audio book" has been synonymous with
"books on tape" for roughly 20 years. Cassette tape sales still comprise roughly 40% of the audio book market, with CDs the other dominant format type.

Unabridged audio books are word for word readings of a book, while abridged audio books have text edited out by the abridger. Audio books also come as fully dramatized versions of the printed book, sometimes calling upon a complete cast, music and sound effects.
(http://en.wikipedia.org/wiki/Audiobook )

Sample created by an actor or performing artist. Used in casting processes to demonstrate the performer's talent. It is considered to be the job interview for the performer. An example of it is the recording of a piece of audio containing a previously given script to display someone's talent.

Automated dialogue replacement or Additional dialogue recording (ADR) is a film sound technique involving the re-recording of dialogue after photography, also known as "looping" or a looping session.[1] In the UK it is called post-synchronisation orpost-sync. ADR is recorded during an ADR session. An actor, usually the original actor on set, is called to a sound studio equipped with video playback equipment and sound playback and recording equipment. The actor wears headphones and is shown the line of the film that must be replaced, and often he or she will be played the production sound recording. The film is then projected several times, and the actor attempts to re-perform the line while watching the image on the screen, while an ADR Recordist records the performances. Several takes are made, and based on the quality of the performance and sync, one is selected and edited by an ADR Editor for use in the film.
(http://en.wikipedia.org/wiki/Dubbing_(filmmaking) )