(FLAC) Stands for Free Lossless Audio Codec, an audio format similar to MP3, but lossless, meaning that audio is compressed in FLAC without any loss in quality. This is similar to how Zip works, except with FLAC you will get much better compression because it is designed specifically for audio, and you can play back compressed FLAC files in your favorite player (or your car or home stereo, see supported devices) just like you would an MP3 file.
The Apple Lossless Audio Codec (ALAC) is an audio codec developed by Apple and supported on iPhone, iPad, most iPods, Mac and iTunes. (ALAC) is a data compression method which reduces the size of audio files with no loss of information.

What is Apple Lossless format?
Apple Lossless, also known as Apple Lossless Audio Codec (ALAC), or Apple Lossless Encoder (ALE), is an audio coding format, and its reference audio codec implementation, developed by Apple Inc. for lossless data compression of digital music.

Is Apple lossless m4a?
Apple Lossless data is stored within an MP4 container with the filename extension .m4a. This extension is also used by Apple for lossy AAC audio data in an MP4 container (same container, different audio encoding).

Advanced Audio Coding (AAC) is an audio coding standard for lossy digital audio compression. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates.

What is an AAC file in itunes?
AAC is the default format used by iTunes. It produces better audio quality than MP3 for a given data rate (e.g., 128 kbps) and is playable in almost all software that can play MP3 files.

Constant bit rate (CBR) encoding persists the set data rate to your setting over the whole video clip. Use (CBR) only if your clip contains a similar motion level across the entire duration. (CBR) is most commonly used for streaming video content using the Flash Media Server (rtmp)

Variable bit rate (VBR) encoding adjusts the data rate down and to the upper limit you set, based on the data required by the compressor. (VBR) takes longer to encode but produces the most favorable results. (VBR) is most commonly used for http delivery if video content (http progressive)

(VBR) stands for Variable BitRate. As with (VBR) video encoding, the idea is that the encoder uses only the bitrate required to encode the data, usually based around a minimum, maximum and average value. The result can be higher quality at the same average bitrate as (CBR), or the same quality as (CBR) at a lower average bitrate.

(CBR), or Constant BitRate, uses a single bitrate regardless of the needs of the track.

(CBR), on the other hand, is pretty universal, and any MP3 device will happily read and play (CBR) encoded files.